A new approach to species distributional indicators for the Marine Strategy Framework Directive (MSFD)

We propose alternative fish-populations spatial indicators for use in the Marine Strategy Framework Directive (MSFD). Following Commission Decision 2010/477, we have applied two different spatial indicators to three fish populations with “slow type” life-history traits, i.e. slow growing like Helicolenus dactylopterus, or large bodied like Merluccius merluccius and Lophius budegassa. We tested their efficiency separately and combined. One of these indicators, the presence/absence of the population in sampling squares, had already been applied during the initial assessment of the MSFD in Spain. Another indicator, the geographical spread, is proposed here as a new monitoring tool for the MSFD in Spanish waters. The results demonstrate for the three populations analyzed that neither indicator was sufficient alone to describe the population spatial pattern or its evolution. Thus, the approach to implementing the MSFD indicated in Commission Decision 2010/477 is not sufficient to provide integrated information about the spatial behavior of the fish populations analyzed. Although numerical targets or threshold values cannot be set, directional targets could be proposed, based on the results of both indicators, if evaluation of them is extended to more species and more geographical areas. The analysis could be extended to other “slow type” populations within the fish community and also to different ecoregions. We propose an approach including the estimation of two different indicators to monitoring both the area occupied and the geographical spread of fish populations within communities, interpreting them together to generate a more complete picture of the spatial patterns of those populations. In spite of the difficulties in fixing numerical targets or thresholds, or in distinguishing between environmentally and human driven changes in the population spatial distributions, this approach helps to summarize fish spatial behavior. It improves information from the indicators applied alone and reduces the requirement for a large number of maps (except for some particular event or population). The proposed indicators can be readily used by managers and politicians.     

Indicators of the Ecological Impact of Bottom-Trawl Disturbance on Seabed Communities

The Ecosystem Approach to Fisheries requires that managers take account of the environmental impacts of fishing. We develop linked state and pressure indicators that show the impact of bottom-trawling on benthic communities. The state indicator measures the proportion of an area where benthic invertebrate biomass (B) or production (P) is more than 90% of pristine benthic biomass (B _0.9) or production (P_0.9). The pressure indicator measures the proportion of the area where trawling frequency is sufficiently high to prevent reaching predicted B_0.9 or P_0.9. Time to recovery to B_0.9 and P_0.9 after trawling, depending on the habitat, was estimated using a validated size-based model of the benthic community. Based on trawling intensity in 2003, 53.5% of the southern North Sea was trawled too frequently for biomass to reach B_0.9, and 27.1% was trawled too frequently for production to reach P_0.9. As a result of bottom-trawling in 2003, in 56% of the southern North Sea benthic biomass was below B_0.9, whereas in 27% of the southern North Sea benthic production was below P_0.9. Modeled recovery times were comparable to literature estimates (2.5 to more than 6 years). The advantages of using the area with an ecological impact of trawling as a pressure indicator are that it is conceptually easy to understand, it responds quickly to changes in management action, it can be implemented at a relevant scale for fisheries management, and the necessary effort distribution data are centrally collected. One of this approach’s greatest utilities, therefore, will be to communicate to policy makers and fishing enterprises the expected medium- to long-term ecological benefits that will accrue if the frequency of trawling in particular parts of fishing grounds is reduced.     

Modeling the spatial distribution of the striped dolphin (Stenella coeruleoalba) and common bottlenose dolphin (Tursiops truncatus) in the Gulf of Taranto (Northern Ionian Sea,Central-eastern Mediterranean Sea)

Although the EU Marine Strategy Framework Directive (MSFD) is largely based on the establishment of environmental targets and associated proxies to achieve Good Environmental Status (GES), a full suite of ecological indicators for all the ecosystem components is not currently available for ongoing assessment and regular update of GES targets. This is because effective indicators and management actions aimed at preserving/rebuilding marine biodiversity should be found from the knowledge of the spatial distribution of target species and extension of critical habitats as well as their overlapping with human activities, pressure and impacts. In this regard, the spatial distributions of the striped dolphin Stenella coeruleoalba and the common bottlenose dolphin Tursiops truncatus in the Gulf of Taranto (Northern Ionian Sea, Central-eastern Mediterranean Sea) were investigated by means of a generalized additive model (GAM) and a Random Forest (RF) based on sighting data collected during standardized vessel-based surveys carried out from 2009 to 2015. Eight predictive variables were considered, taking into account both the local physiographic features and human activities existing in the investigated area, suggesting an innovative approach to habitat modeling. In particular, the explanatory variables depth, distance from industrial areas and distance from the coast proved to significantly influence the distribution of both dolphin species. In addition, the distribution of S. coeruleoalba and T. truncatus were also significantly shaped by the distance from the navy exercise areas and the fishing areas, respectively. On the contrary, the slope and the distance from the main commercial routes never provided any significant influence. The reliability of GAM and RF models in predicting the spatial distribution of both dolphins was tested by applying the Youden Index method to the ROC curves. The RF model allowed the projection of the expected presence/absence pattern of S. coeruleoalba and T. truncatus to produce the preference habitat versus non habitat map. In particular, the RF model predicted that the striped dolphin is widely present in the central and deeper part of the Gulf of Taranto. In contrast, the common bottlenose dolphin seems to be mainly distributed along the coasts in both the eastern and western sector of the basin. A clear overlapping of the preference habitats estimated for S. coeruleoalba and T. truncatus is shown north of Punta Alice and in front of Policoro as well as offshore from Ugento in the eastern and western parts of the investigated area, respectively. Finally, the critical habitats of S. coeruleoalba and T. truncatus are the outcome of both the influence of environmental conditions and anthropogenic pressures presently occurring in the Gulf of Taranto, basically indicating the need for conservation measures, especially considering that the area is expected to be considered for hydrocarbon prospecting. These results contribute to setting up a baseline reference for future assessment of environmental marine disturbances using cetaceans, which are considered a key group in the MSFD, as an ecological indicator.     

Characterizing fishing effort and spatial extent of coastal fisheries

Biodiverse coastal zones are often areas of intense fishing pressure due to the high relative density of fishing capacity in these nearshore regions. Although overcapacity is one of the central challenges to fisheries sustainability in coastal zones, accurate estimates of fishing pressure in coastal zones are limited, hampering the assessment of the direct and collateral impacts (e.g., habitat degradation, bycatch) of fishing. We compiled a comprehensive database of fishing effort metrics and the corresponding spatial limits of fisheries and used a spatial analysis program (FEET) to map fishing effort density (measured as boat-meters per km2) in the coastal zones of six ocean regions. We also considered the utility of a number of socioeconomic variables as indicators of fishing pressure at the national level; fishing density increased as a function of population size and decreased as a function of coastline length. Our mapping exercise points to intra and interregional 'hotspots' of coastal fishing pressure. The significant and intuitive relationships we found between fishing density and population size and coastline length may help with coarse regional characterizations of fishing pressure. However, spatially-delimited fishing effort data are needed to accurately map fishing hotspots, i.e., areas of intense fishing activity. We suggest that estimates of fishing effort, not just target catch or yield, serve as a necessary measure of fishing activity, which is a key link to evaluating sustainability and environmental impacts of coastal fisheries.     

A generic aggregation approach to account for statistical uncertainty when combining multiple assessment results

The one-out-all-out approach (OOAO) for aggregating the assessments of single elements (e.g. species or ecosystem components) has found application in environmental polices such as the European Water Framework Directive or the Marine Strategy Framework Directive (MSFD). However, the OOAO has been challenged as being too pessimistic by making positive assessment results virtually impossible along the increasing number of aggregated elements. This study presents a generic approach, the probabilistic One-out-all-out approach, (pOOAO), to account for this issue and thereby reconciling the OOAO with probabilistic aggregation methods The pOOAO allows to determine the minimum number of elements (K_GES), which should meet their assessment benchmarks and thus should achieve a good status. By pre-setting a generic confidence level for each single assessment (e.g. 0.95) the binomial distribution can be used to obtain K_GES for any number of assessed elements. The pOOAO can also accommodate for the integration of assessments from multiple indicators within an element by adjusting the confidence level in relation to the number of integrated indicators. Depending on the generic confidence level as well as on the number of and integrated indicators and aggregated elements, the pOOAO is either consistent with the OOAO or allows for a certain number of negative assessment results, which are attributed to statistical uncertainty and error propagation. The pOOAO is consistent with the OOAO if the desired confidence level in the single assessment results is very high (>0.99) and/or the number of aggregated elements and integrated indicators is low. Through this flexibility the pOOAO could find wide application within integrated ecosystem assessments frameworks such as the MSFD, but would require to estimate the confidence level for each single assessment.     

Indicators of seabird reproductive performance demonstrate the impact of commercial fisheries on seabird populations in the North Sea

In a world of growing anthropogenic pressures on biodiversity, effective indicators need to be specific and sensitive to the pressures in the ecosystem concerned, yet be simple enough to be interpreted by non-experts and straightforward enough to facilitate routine monitoring. Globally, seabirds are under increasing pressure as a result of anthropogenic activities and environmental variation. Traditionally, seabird indicators have been based on abundance at breeding colonies. However, as many species do not reach sexual maturity for several years, and may not attend the colony over this time period, such indicators may fail to capture the ecological complexity of the system concerned.We constructed two indicators of the state of nine seabird species that breed along the UK coast of the North Sea: (i) abundance of seabirds at breeding colonies, and (ii) probability of seabird breeding failure. The indicators were significantly and strongly correlated with each other for eight out of nine species, but the abundance indicator typically lagged the indicator on seabird breeding failure by two to three years. We then considered a third indicator which compared kittiwake (Rissa tridactyla) breeding success to the levels expected given the underlying environmental conditions; changes in the abundance indicator also lagged this by three years. We investigate how sensitive each of these indicators was to the impacts of fishing. We found that the species which had seen the greatest increases in breeding failure rate over the study period were those species which were most sensitive to fisheries pressure.By focussing on demographic parameters, and correcting for the underlying environmental conditions, we can detect potentially important population level changes at an earlier stage than by focussing on abundance alone. These indicators are able to more accurately capture the complexity of the ecosystem concerned and can be readily interpreted by policy-makers.     

Fishing-induced changes in predation pressure by perch (<Emphasis Type="Italic">Perca fluviatilis</Emphasis>) regulate littoral benthic macroinvertebrate biomass,density, and community structure

We aimed to study whether the varying changes in predation pressure by perch (Perca fluviatilis) reflect the biomass, density, and community structure of the benthic macroinvertebrates. Prey preference is size-dependent, and overall predation pressure is density dependent, and thus the size structure of the P. fluviatilis population should affect the structure of the macroinvertebrate community, and the population density of P. fluviatilis should reflect the overall density of benthic macroinvertebrates. We sampled the littoral benthic community in a boreal lake that had been divided into two parts that were subjected to two different fishing procedures during 2007–2012 period and analyzed the macroinvertebrate diet of fish. The benthic macroinvertebrate community reflected the predation pressure. Total macroinvertebrate biomass increased during the study period in the lake division with a non-size-selective fishing procedure (NSF), i.e., all invertivorous perch size-classes targeted, but decreased in the section with negatively size-selective fishing procedure (SSF), i.e., large invertivorous individuals ≥ 16 cm were not targeted. This difference was a result of the increase in large-sized species, such as Odonata, for the NSF procedure and decrease in the SSF procedure. In contrast to total biomass, total macroinvertebrate density did not show a response to predator size structure but rather total macroinvertebrate density decreased with increasing fish density. The study demonstrates the effect of predation pressure of P. fluviatilis on benthic communities, thus highlighting the keystone predator role of the species in boreal lakes and gives more insight on the multiple effects of fish predation on littoral benthic communities.     

Food-web indicators accounting for species interactions respond to multiple pressures

Food-web indicators for marine management are required to describe the functioning and structure of marine food-webs. In Europe, the Marine Strategy Framework Directive (MSFD), intended to lead to a ‘good environmental status’ of the marine waters, requires indicators of the status of the marine environment that also respond to manageable anthropogenic pressures. Identifying such relationships to pressures is particularly challenging for food-web indicators, as they need to be disentangled from linkages between indicators of different functional groups caused by species interactions. Still, such linkages have not been handled in the indicator development. Here we used multivariate autoregressive time series models to identify how fish indicators in an exploited food-web relate to fishing, climate and eutrophication, while accounting for the linkages between indicators caused by species interactions. We assembled 31-year long time series of indicators of key functional groups of fish in the Central Baltic Sea pelagic food-web, which is characterized by strong trophic links between cod (Gadus morhua) and its main fish prey sprat (Sprattus sprattus) and herring (Clupea harengus). These food-web indicators were either abundance-based indicators of key piscivores (cod) and zooplanktivores (sprat and herring) or size-based indicators of the corresponding trophic groups (biomass of large predatory fish (cod ≥ 38 cm) and biomass of small prey fish (sprat and herring <10 cm)). Comparative analyses of models with and without linkages among indicators showed that for both types of indicators, linkages corresponding to predator-prey feedbacks and intra-specific density-dependence were essential to explain temporal variation in the indicators. Thus, no indicator-pressure relationships could be found that explained the indicators’ variation unless such linkages were accounted for. When accounting for these, we found that the indicators overall respond to multiple pressures acting simultaneously rather than to single pressures, as no pressure alone could explain how the indicators developed over time. The manageable pressures fishing and eutrophication, as well as the prevailing hydrological conditions influenced by climate, were all needed to reproduce the inter-annual changes in these food-web indicators combined, although individual relationships differed between the indicators. We conclude that our innovative indicator-testing framework can therefore be used to identify responses of food-web indicators to manageable pressures while accounting for the biotic interactions in food-webs linking such indicators.     

Ringed seal (Pusa hispida) tooth annuli as an index of reproduction in the Beaufort Sea

Multi-decadal time-series of biological indices that reflect the state of a population are rare in ecological studies, but invaluable for assessing environmental regulation of population dynamics. We utilized canine teeth extracted from ringed seals (Pusa hispida) killed by polar bears (Ursus maritimus) in the Beaufort Sea, Canada, in 1985–2011, to obtain widths of annual growth layers in the cementum. Canine teeth for 75 individuals were measured and compared across years using a proportional width index (PWI) spanning 1965–2007. PWI was positively correlated with ringed seal ovulation rate obtained independently from other studies and was significantly lower than normal during ringed seal reproductive declines in 1974–75, 1984–87, 1991–93, and 2004–05, suggesting that PWI reflects ringed seal reproductive capacity. The PWI was also examined against climatic and sea ice factors to assess environmental regulation of ringed seal reproduction. Results suggest that ringed seals benefit from cyclonic circulation regimes in the Beaufort Sea, and an earlier breakup of sea ice in summer that may positively influence the quality and quantity of food during the open water season. Results highlight how cementum annuli in the canine teeth of ringed seals can provide an index of body state and linkages to sea ice conditions. Canine teeth from ringed seals can function as a means to monitor the effects of past Arctic marine variability on area-specific populations for which there are few independent empirical data.     

Dynamics and the state of fishery resources in the Rybinsk Reservoir from 1950–2010

Data on dynamics of the main commercial fish populations in the Rybinsk Reservoir over the period of 1950–2010 have been generalized. Fishing intensity is the main factor that determines the state of fish resources. It affects not only the abundance of commercial fish but also determines changes in population characteristics, i.e., changes in age and size structure and increase in the portion of young individuals. The effect of fishing on populations of some species depends on their commercial value. Commercial fishing affects notably such species as bream Abramis brama, zander Sander lucioperca, and pike Esox lucius. Commercial fishing affects, to a lesser extent, populational characteristics of such mass fish species as roach Rutilus rutilus and blue bream Abramis ballerus whose commercial value is lower.     

Population Growth in Planaria Dugesia tigrina (Gerard) : Regulation by the absolute number in the population

Planaria reproduce by transverse fission. Isolated worms increase in number exponentially, while social animals at the same density are inhibited in terms of numerical increase, but over a 25 day period undergo a larger increase in mass. Isolated posterior fission products reproduce faster than isolated anterior fission products. Regulation of population growth is independent of density over a 16-fold range and regulatory factors cannot be demonstrated in the medium. Regulation of population growth depends on direct contact between animals. Fission period varies from individual to individual and from period to period for a given individual. Doubling time is related to the absolute number of individuals comprising the population as follows: P_N = (P_M · N)/(K + N), where P_N is the doubling period of a population of N individuals, P_M is the doubling time of an infinitely large population, N is the number of individuals in the population, and K is the number of individuals in a population the period of which is one-half P_M. At 22°–24°C P_M is estimated to be 43.3 days and K is 1.87 individuals. A model system assumes that inhibitor flows through the population from animal to animal from the slowest to the fastest animal in the population thus acting to synchronize population increase as well as to determine the rate of population growth. A possible source of the inhibitor is discussed.     

Spatial indicators of fishing pressure: Preliminary analyses and possible developments

Ecological indicators of fishing pressure in space are an important part of the Data Collection Framework (DCF) established by the European Commission in its attempt to apply an ecosystem approach to fisheries. These indicators are devised to use the information provided by the Vessel Monitoring System, a mandatory tool for EU fishing vessels which allows to record fishing activity in space and time. This study reports and analyzes trends of DCF fishing pressure indicators in the years 2007–2010 for the Italian trawlers in seven Mediterranean geographic sub-areas and the related trends of landing per unit effort. In addition, new versions of these indicators are developed and their performances compared to the DCF ones by a simulation approach. The rationale for these new version of indicators is based on: (i) the development of a formal definition of “fishing ground”, allowing for innovative statistical analyses of fishing patterns in space and time; (ii) the revision of issues affecting DCF indicators. Results provide: (i) the first extensive documentation of space use by fisheries through time; (ii) evidences of subtle yet significant changes in fishing pattern which, in agreement to other studies, indirectly support a decline of fisheries resources in the Mediterranean; (iii) improved versions of DCF fishing pressure indicators, obtained via the identification and analysis of fishing grounds and the assessment of aggregation by Gini's G index. The latter point could mark an important progress in order to overcome some critical weakness evidenced by DCF indicators. Moreover, the statistical identification and analysis of fishing grounds could represent a valuable insight in quantitative investigations of fisheries impacts and effects, even beyond indicators computation.     

Amazonian invaders in an Asian biodiversity hotspot: Understanding demographics for the management of the armoured sailfin catfish,Pterygoplichthys pardalis in Kerala,India

Invasion of armoured catfish, Pterygoplichthys spp., is a major threat to global aquatic biodiversity, and developing effective strategies for their control and eradication is both a concern and a research priority. A length-based population assessment of invasive Pterygoplichthys pardalis in southern India, a hotspot for endemic aquatic biodiversity, indicated that rapid growth, high growth performance index and continuous recruitment have aided their successful invasion. Increasing fishing pressure on the adults is not adequate for population management, and only targeting young individuals (<30 cm) will result in overexploitation and population collapse.     

Determining the linkage of disease-resistance genes to molecular markers: the LOD-SCORE method revisited with regard to necessary sample sizes

Some approaches to molecular marker-assisted linkage detection for a dominant disease-resistance trait based on a segregating F₂ population are discussed. Analysis of two-point linkage is carried out by the traditional measure of maximum lod score. It depends on (1) the maximum-likelihood estimate of the recombination fraction between the marker and the disease-resistance gene locus, (2) the observed absolute frequencies, and (3) the unknown number of tested individuals. If one replaces the absolute frequencies by expressions depending on the unknown sample size and the maximum-likelihood estimate of recombination value, the conventional rule for significant linkage (maximum lod score exceeds a given linkage threshold) can be resolved for the sample size. For each sub-population used for linkage analysis [susceptible (= recessive) individuals, resistant (= dominant) individuals, complete F₂] this approach gives a lower bound for the necessary number of individuals required for the detection of significant two-point linkage by the lod-score method.     

Assessing eutrophication in the Portuguese continental Exclusive Economic Zone within the European Marine Strategy Framework Directive

This study reports the state and causes of eutrophication in the Portuguese continental Exclusive Economic Zone (EEZ), during a 14-year period (1995–2008), following the European Marine Strategy Framework Directive (MSFD) and using the trophic index TRIX for an integrated evaluation of indicators of eutrophication, and identifies areas where monitoring is needed to improve the eutrophication assessment. A non-continuous dataset for the 8 indicators specified by the MSFD for eutrophication assessment was used, including published and grey data. Eutrophication indicators were validated and thresholds reviewed, considering regional differences. The diatom:flagellate ratio was found a poor indicator of eutrophication as shifts in the diatom:flagellate ratio naturally occur associated with alternating water column turbulence and upwelling, and stratification, and therefore, could not be associated with anthropogenic nutrient enrichment effects. Assessment areas were, as a whole, classified as non-problem areas concerning eutrophication. Although nutrient enrichment was observed in coastal waters, related to river plume influence, nutrient enrichment direct and indirect effects were generally not detectable, possibly due to water column dispersion and mixing processes. Only occasionally, mild eutrophication was found in specific areas under the influence of major river (Douro, Vouga and Guadiana) plumes, associated with high nutrient and phytoplankton biomass levels and seagrass decline, which indicates the need for directed monitoring on eutrophication in those areas.     

Effects of commercial fishing on the population structure of spawning southern calamary (Sepioteuthis australis)

This study explored population dynamics of Sepioteuthis australis on a fine temporal scale before, during, and after a 3-month commercial fishing closure on the summer inshore spawning grounds of Great Oyster Bay, Tasmania, Australia. An abrupt change in male size (mantle length) and population sex ratio after the re-opening of the commercial fishery suggests that fishing alters the population structure on the spawning beds from a ‘natural’ structure which is highly biased towards males, to a more even ratio of males to females. Although jigs are taking a representative sample of the squid population using the spawning beds at any one time, the fishery is apparently still effectively selective for males, potentially as a function of differential spawning movements of the two sexes. Increased fishing pressure over the past 5 years had been correlated with a change towards a highly male-biased sex ratio on the spawning beds; however the current study suggests that increased fishing pressure in recent years may not have reduced the proportion of females. Instead, the inter-annual change in sex ratio may reflect changes in the degree of protection from fishing, with progressively longer closures allowing time for more males to accumulate on the beds and therefore, for the proportion of males to increase (as opposed to a decrease of females). As fishing is selective for males, fishing throughout the spawning season could potentially modify the process of sexual selection and the mating behaviors of the individuals within the spawning population, highlighting the need for closures over this crucial period. Additionally, examinations and comparisons of squid population structure need to be interpreted in light of fishing pressure and broader movement patterns.     

Size-spectra as indicators of the effects of fishing on coral reef fish assemblages

The data requirements and resources needed to develop multispecies indicators of fishing impacts are often lacking and this is particularly true for coral reef fisheries. Size-spectra, relationships between abundance and body-size class, regardless of taxonomy, can be calculated from simple sizeabundance data. Both the slope and the mid-point height of the relationship can be compared at different fishing intensities. Here, we develop size-spectra for reef fish assemblages using body size- abundance data collected by underwater visual census in each of ten fishing grounds across a known gradient of fishing intensity in the Kadavu Island group, Fiji. Slopes of the size-spectra became steeper (F_9,69=3.20, p<0.01) and the height declined (F_9,69=15.78, p<0.001) with increasing fishing intensity. Regressions of numbers of individuals per size class across grounds were negative for all size classes, although the slope was almost zero for the smallest size class. Response to exploitation of each size class category was greatest for larger fish. Steepening of the slope with increasing fishing intensity largely resulted from reductions in the relative abundance of large fish and not from the ecological release of small fish following depletion of their predators. The slope and height of the size-spectrum appear to be good indicators of fishing effects on reef fish assemblages.     

Genetic diversity and population structure of Sepiella japonica (Mollusca: Cephalopoda: Decapoda) inferred by mitochondrial DNA (COI) variations

In order to describe the genetic diversity of five geographical populations of cuttlefish (Sepiella japonica) along with Chinese coast and determined their phylogenetic relationship, partial mitochondrial COI gene (681bp in length) was amplified from 96 individuals collected from these populations and sequenced. The 5 populations of cuttlefish inhabit Yellow Sea, East China Sea and South China Sea. Out of 22 polymorphic nucleotides identified, 8 were represented by a single sequence, 12 were parsimony informative, which defined 22 haplotypes. Haplotype and nucleotide diversity were low among populations. Of 22 haplotypes, 15 appeared only in a single population, 6 appeared in 2 or 3 populations and 1 was shared by all populations. The COI gene was monomorphic in Qingdao population. The haplotypes identified clustered into 2 clades, each covered individuals from 5 populations each. Pairwise F_ST were not proportional to the geographical distances. Among the 5 populations, relatively high level of genetic diversity was found in Ningde population which was recommended to be the best choice of germplasm resources for artificial releasing project.     

Demographics of Lagocephalus inermis in the Arabian Sea unveils complex conservation challenges

The first assessment of the demographics of Lagocephalus inermis, a species associated with pufferfish bites and fishing down the food web in the Arabian Sea, south-west coast of India, was performed based on length structured population dynamics of 1601 individuals caught in commercial fisheries. Analysis revealed that the current level of exploitation is 90% of the predicted exploitation producing maximum relative yield per recruit (E_max), suggesting high levels of exploitation with potential for significant negative consequences for trophic cascades.