Demersal fish assemblages on seamounts exploited by fishing in the Azores (NE Atlantic)

Seamount fish communities are susceptible to variations due to the oceanographic conditions and level of historical fishing effort. In the NE Atlantic, the Azores is considered an “oceanic seamount ecosystem area” because seamount concentration is high relative to other regions. Scientific information on seamounts in the Azores remains scarce and demersal fishery occurs mostly without any knowledge to endorse sustainable harvest strategies. To make available an important baseline information on dynamics of demersal fish populations inhabiting commercially exploited seamounts, the present study has as specific objectives to (a) describe the taxonomic composition of demersal fish assemblages on underwater mountains, (b) examine whether assemblages vary spatial and temporally, and (c) investigate what drives distributional patterns of species in terms of abundance and size composition. For this, three Azorean seamounts (Açores, Princesa Alice and Mar da Prata) exploited by bottom fishing were selected as case study areas. Data were obtained from scientific surveys and commercial fishery over the past c. 25 years. A total of 84 species from 45 families were identified. Sebastidae, Moridae, Sparidae and Centrophoridae were the most abundant families, mainly represented by Helicolenus dactylopterus, Mora moro, Pagellus bogaraveo and Deania profundorum, respectively. Fish assemblages were more distinguishable spatially than temporally. Depth was identified as the main factor responsible for these differences. The higher occurrence of shallow and intermediate (i.e., up to 600 m) habitats in Princesa Alice and Açores seems to favor the occurrence of a greater number of species and higher abundances in comparison to Mar da Prata. Phycis phycis, Pontinus kuhlii, H. dactylopterus, P. bogaraveo, Conger conger and M. moro were the species which primarily contributed to dissimilarities in assemblage structure among sample groups. Abundance indices and fish sizes showed a decreasing trend for many of these species, especially for those with sedentary behaviour inhabiting historically highly exploited seamount areas. These results highlighted the vulnerability of demersal fishes to the expansion of fishing effort in the offshore seamount areas. Spatial management of seamounts should be a priority being fish conservation balanced with strategies that support sustainable fisheries.     

Can we consider the stocks of alfonsinos Beryx splendens and Beryx decadactylus from the Azores a discrete fishery management unit?

This paper summarises the detailed information on catch, fork length, weight, sex and maturity of alfonsinos Beryx splendens and Beryx decadactylus collected from targeted surveys in Azores waters, complemented by fishery data, over the past c. 20 years. To date, it was not possible to define if the Azorean component of the population can be considered as a discrete local management unit. The reason for this is the lack of available information for these resources covering the entire spatial distribution of the species in the North Atlantic Ocean. Additionally, there are some conflicts between the different genetic results available, poor understanding about the species movements and data from the Azores show some discrepancies in aspects of reproduction. Consequently, there is no analytical assessment for this resource and the stock of Beryx spp. is currently managed based on the precautionary approach. Outputs of recent analyses are presented in this study and possible assumptions and strategies for the assessment are discussed.     

SMART: A Spatially Explicit Bio-Economic Model for Assessing and Managing Demersal Fisheries,with an Application to Italian Trawlers in the Strait of Sicily

Management of catches, effort and exploitation pattern are considered the most effective measures to control fishing mortality and ultimately ensure productivity and sustainability of fisheries. Despite the growing concerns about the spatial dimension of fisheries, the distribution of resources and fishing effort in space is seldom considered in assessment and management processes. Here we propose SMART (Spatial MAnagement of demersal Resources for Trawl fisheries), a tool for assessing bio-economic feedback in different management scenarios. SMART combines information from different tasks gathered within the European Data Collection Framework on fisheries and is composed of: 1) spatial models of fishing effort, environmental characteristics and distribution of demersal resources; 2) an Artificial Neural Network which captures the relationships among these aspects in a spatially explicit way and uses them to predict resources abundances; 3) a deterministic module which analyzes the size structure of catches and the associated revenues, according to different spatially-based management scenarios. SMART is applied to demersal fishery in the Strait of Sicily, one of the most productive fisheries of the Mediterranean Sea. Three of the main target species are used as proxies for the whole range exploited by trawlers. After training, SMART is used to evaluate different management scenarios, including spatial closures, using a simulation approach that mimics the recent exploitation patterns. Results evidence good model performance, with a noteworthy coherence and reliability of outputs for the different components. Among others, the main finding is that a partial improvement in resource conditions can be achieved by means of nursery closures, even if the overall fishing effort in the area remains stable. Accordingly, a series of strategically designed areas of trawling closures could significantly improve the resource conditions of demersal fisheries in the Strait of Sicily, also supporting sustainable economic returns for fishermen if not applied simultaneously for different species.     

Age,growth, mortality and population structure of silver croaker Pennahia argentata (Houttuyn, 1782) and red bigeye Priacanthus macracanthus Cuvier, 1829 in the north‐central Taiwan Strait

The main objectives of this study were to estimate the age, growth, mortality and population structure of silver croaker Pennahia argentata (Houttuyn, 1782) and red bigeye Priacanthus macracanthus Cuvier, 1829 and to explore the factors causing the fluctuation of the fish populations and the ecological parameters. The two species were randomly sampled, with 80~120 individuals of each species captured every month from a single trawler fishery (mesh size 250 mm), March to November 2006, in the north‐central Taiwan Strait. A total of 994 speciments of silver croaker and 851 speciments of red bigeye were collected. Compared with previous studies, the mean length and weight, mean age, the minimum size at first sexual maturity, the asymptotic length (L_∞) and weight (W_∞) of the two species has decreased in recent decades, indicating that the populations were younger, smaller and earlier in sexual maturity. Meanwhile, the growth coefficient (K) increased, the mortality coefficients (Z, F, M) were higher, and the exploitation rate (E) indicated overfishing. Fishing is a key driving force that can cause abundant fluctuations and changes in ecological characteristics in these two demersal fishes in this area. Accordingly, the traditional fishery management approach, such as the reduction in fishing effort, coupled with the Ecosystem‐based Fishery Management (EBFM) should be implemented to achieve sustainable demersal fisheries.     

Longtail tuna,Thunnus tonggol (Bleeker, 1851): a global review of population dynamics,ecology, fisheries,and considerations for future conservation and management

Longtail tuna (Thunnus tonggol) is a neritic species that supports commercial, artisanal and recreational fisheries throughout the Indo-Pacific region. Historically receiving little attention by commercial fisheries, the global annual catch of longtail tuna has steadily risen from around 30,000 t in the early 1980s to exceeding 200,000 t since 2004, reaching a peak of 291,264 t in 2007, and was 281,613 t in 2017. Catches of longtail tuna in the Indian Ocean now exceed catches of principal commercial target species, such as albacore and bigeye tunas. A sequence of stock assessments undertaken throughout the species’ range since the late 1980s persistently indicated that at least three of the four stocks defined in this paper are likely to have been, and most likely are currently, subject to overfishing and overfished as a result of excess fishing effort on this relatively slow-growing and long-lived tuna species. As the spawning biomass of principal tuna target species continue to decline in both the Indian and western and central Pacific Oceans, the increasing catches of longtail tuna, other neritic tunas, and seerfishes is worrisome. Few conservation and management measures (CMMs) are currently in place specifically for longtail tuna, although in recent years some coastal States, Regional Fishery Bodies, and tuna Regional Fisheries Management Organisations have begun to develop initiatives to improve the catch and biological data quality for longtail tuna and sympatric species of neritic tunas and tuna-like species. This paper provides a global review of biological, ecological and fishery information to provide researchers, fishery managers and policy makers with the most current information from which to begin to guide future stock assessment and the development of CMMs for longtail tuna.

     

The decline of the native fishes of lakes Victoria and Kyoga (East Africa) and the impact of introduced species,especially the Nile perch,Lates niloticus,and the Nile tilapia,Oreochromis niloticus

Synopsis There has been a decline, and in some cases an almost total disappearance, of many of the native fish species of lakes Victoria and Kyoga in East Africa since the development of the fisheries of these lakes was initiated at the beginning of this century. The Nile perch, Lates niloticus, a large, voracious predator which was introduced into these lakes about the middle of the century along with several tilapiine species, is thought to have caused the reduction in the stocks of several species. But overfishing and competition between different species also appear to have contributed to this decline. By the time the Nile perch had become well established, stocks of the native tilapiine species had already been reduced by overfishing. The Labeo victorianus fishery had also deteriorated following intensive gillnetting of gravid individuals on breeding migrations. L. niloticus is, however, capable of preying on the species which haven been overfished and could have prevented their stocks from recovering from overfishing. L. niloticus is also directly responsible for the decline in populations of haplochromine cichlids which were abundant in these lakes before the Nile perch became established. Even without predation by Nile perch, it has been shown that the haplochromine cichlids could not have withstood heavy commercial exploitation if a trawl fishery had been established throughout Lake Victoria. Their utilisation for human food has also posed some problems. The abundance of the native tilapiine species may also have been reduced through competition with introduced species which have similar ecological requirements. At present, the Nile perch and one of the introduced tilapiine species, Oreochromis niloticus, form the basis of the fisheries of lakes Victoria and Kyoga.Invited editorial     

Trophic interactions and the diet composition of sympatric finfish predators in the tropical demersal ecosystem in the Bay of Bengal

The dietary composition, foraging strategies, and interspecific trophic interactions were identified for four major demersal carnivorous finfishes, namely, croaker Otolithes ruber, hairtail Trichiurus lepturus, threadfin bream Nemipterus japonicus, and lizardfish Saurida undosquamis, along the north-western part of Bay of Bengal from 2014 to 2016. Two species, Trichiurus lepturus and Saurida undosquamis, were identified as finfish feeders due to the high number of teleost (clupeids and engraulids) prey. One species, Nemipterus japonicus, had a significantly different diet of metapenaeids and charybdids, and was identified as a shellfish feeder. The final species, Otolithes ruber, preyed equally on crustaceans and teleosts, and was identified as a shellfish-finfish feeder. The feeding activity of all four species was lower during peak spawning periods and tended to increase with maturity. Feeding preferences varied with seasons. The trophic level ranged from 3.49 to 4.01, classifying the four species as medium-carnivores or meso-predators. Niche breadth ranged from 0.170 to 0.421, with seasonal and ontogenetic variations. Individual or subgroup specialization was observed on dominant prey, but intraspecific diet variations indicated all four species to be opportunistic predators. There was substantial prey overlap for Saurida undosquamis with Otolithes ruber and Trichiurus lepturus, which increased ontogenetically and coincided with their peak spawning. Sharing of abundant prey resources together with temporal and ontogenetic resource partitioning at intra- and interspecific levels possibly lowered dietary competition, thereby facilitating the coexistence of these demersal predators. This study provides new information on feeding interactions from a tropical demersal ecosystem that can be applied for the ecosystem-based management of trawl fisheries.     

A dataset from bottom trawl survey around Taiwan

Bottom trawl fishery is one of the most important coastal fisheries in Taiwan both in production and economic values. However, its annual production started to decline due to overfishing since the 1980s. Its bycatch problem also damages the fishery resource seriously. Thus, the government banned the bottom fishery within 3 nautical miles along the shoreline in 1989. To evaluate the effectiveness of this policy, a four year survey was conducted from 2000-2003, in the waters around Taiwan and Penghu (Pescadore) Islands, one region each year respectively. All fish specimens collected from trawling were brought back to lab for identification, individual number count and body weight measurement. These raw data have been integrated and established in Taiwan Fish Database (http://fishdb.sinica.edu.tw). They have also been published through TaiBIF (http://taibif.tw), FishBase and GBIF (website see below). This dataset contains 631 fish species and 3,529 records, making it the most complete demersal fish fauna and their temporal and spatial distributional data on the soft marine habitat in Taiwan.     

Life-history,exploitation and extinction risk of the data-poor Baraka's whipray (Maculabatis ambigua) in small-scale tropical fisheries

The Baraka's whipray (Maculabatis ambigua) is a major constituent of small-scale fisheries catch in the south-western Indian Ocean. Despite this, little is known of its life-history or exploitation status. We provide the first estimates of crucial life-history parameters and the maximum intrinsic population growth rate r_max , using specimens collected from small-scale fisheries landings in Kenya, Zanzibar and Madagascar (with northern Madagascar representing a range extension for this species). We assess the relative risk of overexploitation by combining r_max with estimates of total Z , fishing F , and natural M mortality, and an estimate of the exploitation ratio E . The data indicate that Baraka's whipray is a medium-sized, fast-growing, early maturing species, with a relatively long lifespan. This results in a high r_max relative to many other elasmobranchs, which when combined with estimates of F suggests that the species is not at imminent risk of extinction. Yet, estimates of exploitation ratio E indicate likely overfishing for the species, with full recruitment to the fishery being post-maturation and exploitation occurring across a broad range of age and size classes. Thus, Baraka's whipray is unlikely to be biologically sustainable in the face of current fisheries pressures. This paper makes an important contribution to filling the gap in available data and is a step towards developing evidence-based fisheries management for this species. Further, it demonstrates a simple and widely applicable framework for assessment of data-poor elasmobranch exploitation status and extinction risk.     

Shared Stocks of Snappers (Lutjanidae) in Australia and Indonesia: Integrating Biology, Population Dynamics and Socio-Economics to Examine Management Scenarios

Joint Australia–Indonesia scientific workshops on the fisheries of the Arafura Sea, held in 1992 and 1994, concluded that the two countries might share stocks of the red snappers Lutjanus malabaricus and L. erythropterus and the gold-band snapper Pristipomoides multidens. At that time, no information concerning stock structure, distribution and movements of these species was available. Moreover, data on the population biology and on commercial catches were inadequate. Such data are crucial for stock assessment and for managing the stocks. Clearly, if the stocks being fished were shared, joint management would be appropriate. In order to answer the questions related to managing shared stocks, a collaborative research project was initiated by Australia (CSIRO as the lead agency) and Indonesia in 1999. The objectives were firstly, to describe the population dynamics, stock structure and biology of snappers relevant to the management of stocks shared between Australian and Indonesian fisheries; secondly, to characterize the social and financial structures of the Indonesian fishery so they could be taken into account in the development of management strategies; and thirdly, to explore ways of developing complementary management for the long term sustainability of the snapper fisheries. This project finished in 2003 and in this paper we bring together the results of the biological, genetic, population dynamics and socioeconomic research in relation to managing shared stocks in the context of managed versus unmanaged fisheries, small scale and industrial fisheries, and in both developed and developing country regulatory environments. Severe data limitations necessitated an innovative approach making use of comparative analyses, often data-poor values, and the drawing together of fishery dependent and independent data to evaluate the status of the stocks.     

Bio‐economic analysis of the Mar Menor (Murcia,SE Spain) small‐scale lagoon fishery

An integrated fisheries management tool based on a bio‐economic model was applied to the demersal fishery in the Mar Menor coastal lagoon in SE Spain, with the objective of exploring solutions to ensure the sustainability of this activity. The hypothesis is that excess harvesting in recent years by fishers trying to offset growing production costs has led to the inefficient use of lagoon fishery resources. The authors established the basic bio‐economic conditions of the fishery in 2012 by means of field sampling and personal interviews with producers, and analyzed the response of several biological and economic indicators (target species biomass and yield, fleet profits) to a management scenario based on limiting the fishing season of one of the main types of fishing gear (fish traps, locally known as ‘paranzas’). Results show that a reduction in fishing mortality of two overexploited species (Sparus aurata and Lithognathus mormyrus) will help recover the biomass of these stocks by more than 40% as well as increase the economic value of the fishery, with profits increasing by 17% over a 4‐year period.     

The Fishery Performance Indicators: A Management Tool for Triple Bottom Line Outcomes

Pursuit of the triple bottom line of economic, community and ecological sustainability has increased the complexity of fishery management; fisheries assessments require new types of data and analysis to guide science-based policy in addition to traditional biological information and modeling. We introduce the Fishery Performance Indicators (FPIs), a broadly applicable and flexible tool for assessing performance in individual fisheries, and for establishing cross-sectional links between enabling conditions, management strategies and triple bottom line outcomes. Conceptually separating measures of performance, the FPIs use 68 individual outcome metrics—coded on a 1 to 5 scale based on expert assessment to facilitate application to data poor fisheries and sectors—that can be partitioned into sector-based or triple-bottom-line sustainability-based interpretative indicators. Variation among outcomes is explained with 54 similarly structured metrics of inputs, management approaches and enabling conditions. Using 61 initial fishery case studies drawn from industrial and developing countries around the world, we demonstrate the inferential importance of tracking economic and community outcomes, in addition to resource status.     

The take of fish species by seabirds and marine mammals in the Australian Fisheries Zone around Heard Island: the potential for competition with a commercial fishery

. The number of predators from Heard Island foraging in shelf waters, their prey requirements, and the proportion of their diet that was commercial and non-commercial fish were estimated. The calculated annual consumption of commercial fish species varied between 36,360 and 84,166 tonnes. The non-commercial Krefftichthys anderssoni was the preferred prey for most predators, and when its occurrence in diets was low it was replaced by crustaceans and commercial fish species. The estimated annual consumption of Champsocephalus gunnari was approximately 2 and 6 times the highest and lowest estimates respectively of the biomass of this species, obtained from three fisheries research cruises. For Dissostichus eleginoides, the maximum estimate was 28% of the highest estimate of biomass. The current fishery for D. eleginoides will most likely impact on southern elephant seals, whose population decreased by 50% between the 1950s and the 1980s, possibly as a result of overfishing around Iles Kerguelen. Received: 26 January 1998 / Accepted: 20 April 1998     

Management strategies for sustainable invertebrate fisheries in coastal ecosystems of Galicia (NW Spain)

Artisanal coastal invertebrate fisheries in Galicia are socio-economically important and ecologically relevant. Their management, however, has been based on models of fish population dynamics appropriate for highly mobile demersal or pelagic resources and for industrial fisheries. These management systems focus on regulating fishing effort, but in coastal ecosystems activities that change or destruct key habitats may have a greater effect on population abundance than does fishing mortality. The Golfo Artabro was analysed as a representative example of a coastal ecosystem in Galicia, and the spider crab Maja squinado used as a model of an exploited coastal invertebrate, for which shallow coastal areas are key habitats for juvenile stages. The commercial legal gillnet fishery for the spider crab harvests adults during their reproductive migrations to deep waters and in their wintering habitats. Illegal fisheries operate in shallow waters. The annual rate of exploitation is >90%, and <10% of the primiparous females reproduce effectively at least once. A simple spatially-explicit cohort model was constructed to simulate the population dynamics of spider crab females. Yield- and egg-per-recruit analyses corresponding to different exploitation regimes were performed to compare management policies directed to control the fishing effort or to protect key habitats. It was found that the protection of juvenile habitats could allow increases in yield and reproductive effort higher than in the present system, with such protection based in the control of the fishing effort of the legal fishery. Additionally, there is an urgent need for alternative research and management strategies in artisanal coastal fisheries based on the implementation of a system of territorial use rights for fishers, the integration of the fishers into assessment and management processes, and the protection of key habitats (marine reserves) as a basic tool for the regulation of the fisheries.     

Trophic niche partitioning of five skate species of genus Bathyraja in northern and central Patagonia,Argentina

Overexploitation of marine communities can lead to modifications in the structure of the food web and can force organisms like elasmobranchs to change their feeding habits. To evaluate the impact that fisheries have on food webs and on the interactions between species, it is necessary to describe and quantify the diet of the species involved and follow it through time. This study compares the diet of five skate species using the data obtained from the by-catch of the Argentine hake (Merluccius hubbsi) fishery in north and central Patagonia, Argentina. Diet composition was assessed by analysing the digestive tract contents and trophic overlapping between species of the genus Bathyraja: Bathyraja albomaculata, Bathyraja brachyurops, Bathyraja macloviana, Bathyraja magellanica and Bathyraja multispinis. A total of 184 stomachs were analysed. The diets of B. albomaculata and B. macloviana mainly comprised annelids, whereas that of B. brachyurops primarily comprised fish, including hake heads discarded by the fishery. The diets of B. magellanica and B. multispinis were largely based on crustaceans. Despite the morphological similarities and their shared preference for benthic habitats, no complete diet overlaps were found between the different species. These results suggest that these skate species have undergone a process of diet specialisation. This is a common feeding strategy that occurs to successfully eliminate competition when resources are limited, which corresponds to the conditions found in an environment being affected by the pressures of overfishing.     

Sex and reproduction of the alfonsino Beryx splendens (Pisces, Berycidae) from the Macaronesian archipelagos

This paper provides comparative information on the reproductive biology of the alfonsino, Beryx splendens Lowe, 1834, species with commercial interest in the Azores, Madeira and the Canary Islands. A total of 846 individuals from Azores (14.0–42.0 cm fork length), 621 from Madeira (17.2–50.0 cm fork length) and 643 from the Canaries (18.2–38.9 cm fork length) were used for the study. The alfonsino is gonochoric with no evidence of sexual dimorphism. Females are more abundant than males; this dominance probably reflects certain differences in the spatial distribution and/or the catchability of males and females in the Macaronesian archipelagos. The spawning season was distinct for the three Macaronesian areas, with an observed North–South variation in the reproductive period: September–March in the Azores, March–June in Madeira and July–September in the Canary Islands. The size at sexual maturity estimated for Madeira and the Canary Islands is similar (32 and 30 cm fork length, respectively), while for the Azores it is reached at smaller length (23 cm fork length). The differences observed in the size at sexual maturity can be explained by the different exploitation levels in each archipelago. Life‐history parameters of the alfonsino suggest that this species has a specialistic life‐history strategy and fisheries based on this species are more susceptible to growth overfishing and population depletion.     

Reproductive biology of black seabream Acanthopagrus schlegelii,threadfin porgy Evynnis cardinalis and red pargo Pagrus major in the northern South China Sea with consideration of fishery status and management needs

The reproductive biology of three commercially significant seabream species (family: Sparidae) Acanthopagrus schlegelii, Evynnis cardinalis and Pagrus major, taken from Hong Kong and adjacent northern South China Sea (SCS) waters, were investigated for their sexual patterns, spawning seasons, length at maturity and exploitation in relation to their conservation and management status. Histological analysis showed E. cardinalis and P. major to be functionally gonochoristic, the latter having a bisexual juvenile stage and being a rudimentary hermaphrodite. Acanthopagrus schlegelii is a protandric hermaphrodite. Standard length (L_S) at 50% sex change for A. schlegelii is 291 mm. L_S at 50% female maturity for E. cardinalis and P. major are 117 and 332 mm, respectively. For all three species, the spawning period falls between November and March. The study highlights geographical differences in reproductive biology among the species and a paucity of fishery or other population‐related data. While heavy fishing pressure, life‐history characteristics and absence of effective management throughout the geographic ranges of these species make them susceptible to overfishing, they nonetheless appear to be generally more resilient than many other taxa that comprise the multi‐species fisheries of the region, possibly due to their relatively rapid sexual maturation and spatial movement patterns. Overall, however, little is known of the biology, fishing history and current fishery status of sparids in general in the northern SCS and the current study is one of the first to examine such aspects of this family in the region and to consider appropriate management options.     

The dangers of ignoring stock complexity in fishery management: the case of the North Sea cod

The plight of the marine fisheries is attracting increasing attention as unsustainably high exploitation levels, exacerbated by more extreme climatic conditions, are driving stocks to the point of collapse. The North Atlantic cod (Gadus morhua), a species which until recently formed a major component of the demersal fisheries, has undergone significant declines across its range. The North Sea stock is typical of many, with a spawning stock biomass that has remained below the safe biological limit since 2000 and recruitment levels near the lowest on record. Cod within the North Sea are currently managed as a single stock, and yet mounting empirical evidence supports the existence of a metapopulation of regionally variable, genetically distinct, sub-stocks. Applying the same management strategies to multiple stocks that differ in their resilience to exploitation inevitably results in the overfishing and likely collapse of the weaker components. Indeed, recent studies have identified two North Sea spawning stocks that have undergone disproportionally large collapses with very substantial reductions in egg production. Similarly affected cod stocks in the northwest Atlantic have shown little evidence of recovery, despite fishery closures. The possible implications of ignoring sub-structuring within management units for biocomplexity, local adaptation and ecosystem stability are considered.     

基于高通量测序的象山港海域黑鲷(Acanthopagrus schlegelii)食性分析

选取象山港黑鲷个体为研究对象,以18S rDNA为靶标,利用Illumina Miseq高通量测序方法研究黑鲷饵料生物组成特征,分析不同龄组黑鲷的食性异同。通过序列比对,共在黑鲷胃含物中鉴定出41个属中的62种饵料生物,分属9个门,其中节肢动物门（Arthropoda）、绿藻门（Chlorophyta）和软体动物门（Mollusca）是黑鲷饵料生物的优势组成门类。从饵料生物相对丰度和出现频率上分析,石莼（Ulva lactuca）、熊本牡蛎（Crassostrea sikamea）、胸刺水蚤（Centropages hamatus）、日本蟳（Charybdis japonica）、毛蚶（Scapharca subcrenata）和褐菖鲉（Sebastiscus marmoratus）是黑鲷的优势饵料物种,所占饵料生物总相对丰度的比重达60.90%。相似性分析检验（ANOSIM）结果显示：1至4龄黑鲷个体的饵料生物组成不存在显著性差异。与传统食性分析方法相比,高通量测序法在黑鲷饵料生物检测灵敏性上显现了较为明显的优势,保障黑鲷等重要物种的种群稳定对于该海域具有重要的生态和经济意义。     

Small-Scale Spatial Variation in Population Dynamics and Fishermen Response in a Coastal Marine Fishery

A major challenge for small-scale fisheries management is high spatial variability in the demography and life history characteristics of target species. Implementation of local management actions that can reduce overfishing and maximize yields requires quantifying ecological heterogeneity at small spatial scales and is therefore limited by available resources and data. Collaborative fisheries research (CFR) is an effective means to collect essential fishery information at local scales, and to develop the social, technical, and logistical framework for fisheries management innovation. We used a CFR approach with fishing partners to collect and analyze geographically precise demographic information for grass rockfish (Sebastes rastrelliger), a sedentary, nearshore species harvested in the live fish fishery on the West Coast of the USA. Data were used to estimate geographically distinct growth rates, ages, mortality, and length frequency distributions in two environmental subregions of the Santa Barbara Channel, CA, USA. Results indicated the existence of two subpopulations; one located in the relatively cold, high productivity western Channel, and another in the relatively warm, low productivity eastern Channel. We parameterized yield per recruit models, the results of which suggested nearly twice as much yield per recruit in the high productivity subregion relative to the low productivity subregion. The spatial distribution of fishing in the two environmental subregions demonstrated a similar pattern to the yield per recruit outputs with greater landings, effort, and catch per unit effort in the high productivity subregion relative to the low productivity subregion. Understanding how spatial variability in stock dynamics translates to variability in fishery yield and distribution of effort is important to developing management plans that maximize fishing opportunities and conservation benefits at local scales.