Seasonal concentrations of reproductive steroids in the gonads of the Atlantic hagfish, Myxine glutinosa

Changes in gonadal morphology, gonadal estradiol, and progesterone were examined in Atlantic hagfish, Myxine glutinosa, during a period of 17 months, beginning in April, 2001. Atlantic hagfish were captured from the ocean on a monthly basis. A total of 60 hagfish were divided into three different size classes of twenty hagfish each (small 20-35 cm, medium 35-45 cm, large 45-55+cm) and transported to the University of New Hampshire for sampling. Overall, in the medium and large size hagfish, estradiol and progesterone had significantly elevated peaks in January, 2001. There were significant increases in estradiol concentrations in January, with relatively low fluctuations in levels for the rest of the sampling period. Progesterone concentrations increased significantly in January, 2002, in medium and large hagfish, and remained elevated until June and April, 2002, for the two size classes respectively. The majority of hagfish sampled were females or hermaphrodites; few true males were identified in any of the samples. The number of females with large eggs increased following the estradiol peak in January and hermaphrodites with mature sperm were identified in the July, 2002, sample. These data represent the first evidence for a seasonal reproductive cycle in M. glutinosa and only the second seasonal reproductive cycle identified in any hagfish species.     

Conservation of Atlantic sturgeon <Emphasis Type="Italic">Acipenser oxyrinchus oxyrinchus</Emphasis>: delineation of stock structure and distinct population segments

The anadromous Atlantic sturgeon Acipenser oxyrinchus oxyrinchus, a wide-ranging species along the Atlantic Coast of North America, is being considered for federal listing under the U.S. Endangered Species Act. Identification of distinct population segments (DPS) is necessary but problematic for highly vagile species such as Atlantic sturgeon which may spend a high proportion of their lives outside of their natal estuaries. Characterization of genetic differentiation and estimates of gene flow provide a quantitative measure of the number of DPS into which species could be divided over their distribution and the reproductive independence of each unit. We sequenced a portion of the mitochondrial DNA control region to characterize population structure and gene flow across all naturally reproducing populations from which specimens could be obtained. We then considered these genetic data along with ancillary information on life history characteristics, historical fisheries data, and trajectories of abundance to determine the number of DPS into which this species should be divided. Our results suggest that philopatry is high for Atlantic sturgeon and that each U.S. estuary analyzed hosts genetically distinct populations of Atlantic sturgeon. We conclude that at least nine DPS of Atlantic sturgeon exist along the Atlantic Coast of the U.S. In contrast, the Atlantic Sturgeon Status Review Team has proposed a five DPS scheme for this subspecies based largely on results from nuclear DNA microsatellites, but with fewer populations represented and lower samples sizes. These different conclusions illustrate the somewhat arbitrary nature of the DPS concept, at least as applied to Atlantic sturgeon.     

Morphometics and Gonadal Development of the Hagfish Eptatretus cirrhatus in New Zealand

Hagfishes have been the target of commercial fisheries in many areas of the world, with the catch processed for leather and for human consumption. A fishery has been operating in New Zealand waters for the last six years, harvesting the bearded hagfish, Eptatretus cirrhatus. The fishery has thus far been unregulated. Based on samples collected dockside over a two-year period, this report expands the morphometric database for this species, provides information on the size and weight of the harvested animals, determines the sizes at the onset of gonadal development and the minimum sizes at sexual maturation for males and females, and indicates that E. cirrhatus, like most other hagfish species, has no specific breeding season. Although females appear in the population at smaller sizes, the sex ratio for mature animals is 1:1 and the sizes of the largest males and females are comparable. The changes observed in sex ratio as a function of TL suggest differences in the timing and rates of gonadal development in females versus males rather than protogyny. Based on the size of the eggs, the number of eggs per female, the proportion of the population that contains large eggs, and the number of postovulatory females, it is clear that E. cirrhatus, like other hagfish species, are potentially vulnerable to overexploitation.     

Novel polymorphic microsatellite loci for a new target species,the sea cucumber Holothuria mammata

With traditional finfish fisheries declining and pushing transition to new invertebrates target species, sea cucumbers have been heavily explored, suffering global overexploitation and worldwide depletion of their stocks.Nowadays, holothurians from the Mediterranean Sea and NE Atlantic Ocean are being exported to Asian markets. The scarce knowledge about their biology, population dynamics, ecology and genetics, is promoting defective management of their fisheries.We report the development of 9 novel polymorphic microsatellites markers for Holothuria mammata and characterized them by testing in three different sample locations. All nine microsatellites revealed high polymorphism and diversity, with high number of alleles, ranged from 11 to 22 and expected heterozygosity, between 0.52 and 0.92. Significant genetic differentiation was found between populations.These microsatellites are providing valuable information which could be applied to fisheries management including, identification of stocks, assessment of their genetic diversity, estimation of gene flow and monitoring the fishery effects on exploited populations.     

Effects of Management Tactics on Meeting Conservation Objectives for Western North American Groundfish Fisheries

There is considerable variability in the status of fish populations around the world and a poor understanding of how specific management characteristics affect populations. Overfishing is a major problem in many fisheries, but in some regions the recent tendency has been to exploit stocks at levels below their maximum sustainable yield. In Western North American groundfish fisheries, the status of individual stocks and management systems among regions are highly variable. In this paper, we show the current status of groundfish stocks from Alaska, British Columbia, and the U.S. West Coast, and quantify the influence on stock status of six management tactics often hypothesized to affect groundfish. These tactics are: the use of harvest control rules with estimated biological reference points; seasonal closures; marine reserves; bycatch constraints; individual quotas (i.e., ‘catch shares’); and gear type. Despite the high commercial value of many groundfish and consequent incentives for maintaining stocks at their most productive levels, most stocks were managed extremely conservatively, with current exploitation rates at only 40% of management targets and biomass 33% above target biomass on average. Catches rarely exceeded TACs but on occasion were far below TACs (mean catch:TAC ratio of 57%); approximately $150 million of potential landed value was foregone annually by underutilizing TACs. The use of individual quotas, marine reserves, and harvest control rules with estimated limit reference points had little overall effect on stock status. More valuable fisheries were maintained closer to management targets and were less variable over time than stocks with lower catches or ex-vessel prices. Together these results suggest there is no single effective management measure for meeting conservation objectives; if scientifically established quotas are set and enforced, a variety of means can be used to ensure that exploitation rates and biomass levels are near to or more conservative than management targets.     

The fishery,biology, and management of Atlantic sturgeon,Acipenser oxyrhynchus,in North America

Synopsis The Atlantic sturgeon supported major fisheries along the entire Atlantic coast of North America. These fisheries peaked about 1890 and then suffered almost total collapse by 1905. The Atlantic sturgeon is anadromous and highly susceptible to capture during spawning migrations. Further, this species biological characteristics makes it very vulnerable to man-induced changes in natural habitat and slow to recover. Atlantic sturgeon mature at an advanced age (7–27 year for females, depending on latitude), exhibit a long interspawning period (2–5 year), and require suitable riverine, estuarine, and coastal environments for successful completion of their life cycle. Today, only remnant stocks exist in areas of former abundance. Management regulations vary considerably from state to state and range from full protection to no protection. Biological data are needed to: identify and characterize specific spawning and nursery areas; delineate migratory patterns and recruitment to various stocks; establish stock abundance; and, assess effects of various management strategies. In order to protect remaining stocks, the imposition of a total harvesting moratorium is recommended.     

Stock identification of the sciaenid fish Micropogonias undulatus in the western North Atlantic Ocean using parasites as biological tags

Proper fisheries management of the Atlantic croaker Micropogonias undulatus is necessary in the United States due to the commercial and recreational importance of this fish species. Croaker stock structure in the western North Atlantic has been investigated in the past by various authors, with inconclusive results. In this study, macroparasites were used as biological tags to identify putative croaker stocks in the area between New Jersey and Florida, which encompasses the Mid Atlantic Bight and the South Atlantic Bight separated at Cape Hatteras, North Carolina. The macroparasite community of the fish was identified, showing the presence of 30 species in four phyla, of which several were new host records, and one species, a monogenean, was new to science. A canonical correspondence analysis was applied to determine the variables responsible for parasite species composition, to resolve the question of croaker stock structure in the western North Atlantic Ocean. This analysis showed that latitude was the deciding variable delineating the parasite community composition of the Atlantic croaker. Among the 30 parasites, 15 were identified as putative tags according to qualitative criteria, and then 10 out of those 15 were selected as being appropriate tags using quantitative criteria. These parasite tags support the presence of two stocks roughly separated at the known biogeographical barrier at Cape Hatteras.     

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     

Restoration of Atlantic sturgeon in the northeastern USA with special emphasis on culture and restocking

Stocks of anadromous Atlantic sturgeon ( Acipenser oxyrhynchus ) on the east coast of the United States are severely depleted due to past over-fishing and habitat loss and degradation. All commercial fisheries for this species are now closed and several state and federal agencies are investigating the use of cultured fish for stock replenishment. A breeding and stocking protocol was developed to address genetic concerns and to provide guidance for culture programs.
Several thousand 3-month old cultured fingerling sturgeon were stocked in the Hudson River, New York, in 1994. Based on mark-recapture techniques, juvenile recoveries in 1995 and 1996 indicated that wild production was very weak in that river. In 1996, several thousand cultured and marked yearling sturgeon were stocked in the Nanticoke River in Maryland. Over the next 10 months, these fish grew well and became distributed throughout the Chesapeake Bay in Maryland and Virginia. The amount of useful information gained from these two examples of using cultured Atlantic sturgeon suggests a broader potential role. Without active intervention, such as a long-term commitment to using cultured fish, some sturgeon stocks on the U. S. Atlantic Coast may be lost.     

Stock composition of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) encountered in marine and estuarine environments on the U.S. Atlantic Coast

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is a large, anadromous fish native to the Atlantic Coast of North America. Although this species once supported important fisheries, centuries of exploitation and habitat degradation have resulted in dramatic declines, presumed extirpation in some rivers, and ultimately listing under the U.S. Endangered Species Act (ESA). Under the ESA, Atlantic sturgeon are listed as five separate Distinct Population Segments (DPSs), which form the basis for federal management. Despite state and federal protections Atlantic sturgeon still face significant threats to their recovery, including fisheries bycatch mortality, marine construction, dredging, dams, and vessel strikes. However, because subadult and adult Atlantic sturgeon migrate extensively across estuarine and marine environments and frequently form mixed-stock aggregations in non-natal habitats, it can be difficult to determine how these threats impact specific populations and DPSs. To better understand ontogenetic shifts in habitat use and stock-specific exposure to anthropogenic threats, we performed a mixed-stock analysis of 1704 Atlantic sturgeon encountered across the U.S. Atlantic Coast. Collections made north of Cape Cod, MA and south of Cape Hatteras, NC were dominated by individuals from regional stocks; however, we found extensive stock mixing in the mid-Atlantic region, particularly in coastal environments where individuals from all five DPSs were commonly observed. Subadults and adults that were encountered in offshore environments had moved, on average, 277 km from their natal source; however, 23% were sampled over 500 km from their natal river suggesting long-distance movements are relatively common in these age classes. Overall, our work highlights that Atlantic sturgeon populations are vulnerable to threats over vast areas and emphasizes the need for continued genetic monitoring to track recovery progress.

     

North American Green and European Atlantic Sturgeon: Comparisons of Life Histories and Human Impacts

Green and European Atlantic sturgeon are listed as a vulnerable and a critically endangered species, respectively. These anadromous species inhabit different continents but have many similar life history traits and demographic characteristics, including wide geographic ranges, similar migratory and foraging behavior, age and size structures of reproductive stocks and, historically, diverse population structures. The differences are limited to tetraploid genome and much larger egg size and lower fecundity in green sturgeon, reflecting the adaptations to different geomorphology and biota of the Pacific region. Both species have been affected by over-harvest and habitat losses but the severity of these impacts have been greater and lasted longer for the European Atlantic sturgeon, resulting in loss of diversity and extirpation of all but one stock. From the comparison of human impact on two species we conclude that preventive actions should be taken at the early warning signs of changes in population and recruitment. These should mitigate multiple factors of human activity affecting sturgeon stocks and their habitats.     

Alligators and Endocrine Disrupting Contaminants: A Current Perspective

Many xenobiotic compounds introduced into the environment byhuman activity have been shown to adversely affect wildlife.Reproductive disorders in wildlife include altered fertility,reduced viability of offspring, impaired hormone secretion oractivity and modified reproductive anatomy. It has been hypothesizedthat many of these alterations in reproductive function aredue to the endocrine disruptive effects of various environmentalcontaminants. The endocrine system exhibits an organizationaleffect on the developing embryo. Thus, a disruption of the normalhormonal signals can permanently modify the organization andfuture function of the reproductive system. We have examinedthe reproductive and developmental endocrinology of severalpopulations of American alligator (Alligator mississippiensis)living in contaminated and reference lakes and used this speciesas a sentinel species in field studies. We have observed thatneonatal and juvenile alligators living in pesticide-contaminatedlakes have altered plasma hormone concentrations, reproductivetract anatomy and hepatic functioning. Experimental studiesexposing developing embryos to various persistent and nonpersistentpesticides, have produced alterations in gonadal steroidogenesis,secondary sex characteristics and gonadal anatomy. These experimentalstudies have begun to provide the causal relationships betweenembryonic pesticide exposure and reproductive abnormalitiesthat have been lacking in pure field studies of wild populations.An understanding of the developmental consequences of endocrinedisruption in wildlife can lead to new indicators of exposureand a better understanding of the most sensitive life stagesand the consequences of exposure during these periods.     

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.     

Injuries from Non-Retention in Gillnet Fisheries Suppress Reproductive Maturation in Escaped Fish

Exploitation of fisheries resources has unintended consequences, not only in the bycatch and discard of non-target organisms, but also in damage to targeted fish that are injured by gear but not landed (non-retention). Delayed mortality due to non-retention represents lost reproductive potential in exploited stocks, while not contributing to harvest. Our study examined the physiological mechanisms by which delayed mortality occurs and the extent to which injuries related to disentanglement from commercial gear compromise reproductive success in spawning stocks of Pacific salmon (Oncorhynchus spp.). We found evidence for elevated stress in fish injured via non-retention in gillnet fisheries. Plasma cortisol levels correlated with the severity of disentanglement injury and were elevated in fish that developed infections related to disentanglement injuries. We also analyzed sex steroid concentrations in females (estradiol-17β and 17,20β-dihydroxy-4-pregnen-3-one) to determine whether non-retention impairs reproductive potential in escaped individuals. We demonstrate evidence for delayed or inhibited maturation in fish with disentanglement injuries. These findings have important implications for effective conservation and management of exploited fish stocks and suggest means to improve spawning success in such stocks if retention in commercial fisheries is improved and incidental mortality reduced.     

Life in 3-D: life history strategies in tunas, mackerels and bonitos

The scombrids (tunas, bonitos, Spanish mackerels and mackerels) sustain some of the most important fisheries in the world and their sustainable management depends on better understanding of their life history strategies. Here, we first assemble life history information on maximum size, growth, longevity, maturity, fecundity and spawning duration and interval for all scombrid species. Second we characterize their life history patterns and trait co-variation and evaluate how many principal axes of trait variation underlie scombrid life history strategies. Most of their life history variation can be explained along three axes or dimensions: size, speed, and reproductive schedule. Body size governs the first axis ranking species along a small-large continuum. The second axis was mostly influenced by time-related traits, such as longevity, growth rates, spawning duration, time between spawning events, ranking species along a slow-fast continuum of life histories. Scombrid species with the slowest life histories such as Atlantic bluefin tuna Thunnus thynnus and Atlantic mackerel Scomber scombrus tend to inhabit more temperate waters while species with faster life histories such as yellowfin tuna Thunnus albacares and short mackerel Rastrelliger brachysoma are typically found in more tropical waters. The third axis comprises the negative relationship between number of eggs produced at length of maturity and rate in gain of fecundity with size describing the schedule of reproductive allocation which reflects a fundamental trade-off between reproduction and growth. Finally, in addition we show that the life history strategies of scombrids conform more closely to the Periodic and Opportunistic strategists within the triangular model of fish life histories.     

Formation of population genetic structure following the introduction and establishment of non-native American shad (<Emphasis Type="Italic">Alosa sapidissima</Emphasis>) along the Pacific Coast of North America

Biological invasions provide opportunities to examine contemporary evolutionary processes in novel environments. American shad, an anadromous fish native to the Atlantic Coast of North America, was introduced to California in 1871 and established spawning populations along the Pacific Coast that may provide insights into the dynamics of dispersal, colonization, and the establishment of philopatry. Using 13 neutral microsatellite loci we genotyped anadromous, freshwater resident and landlocked American shad from 14 locations along the US Pacific Coast to resolve population genetic structure. We observed significant differences in multilocus allele frequency distributions in nearly all (61/66; 92%) pairwise comparisons of non-native anadromous, freshwater resident and landlocked populations, and detected significant genetic differentiation for most (55/66; 83%) of these comparisons. Genetic divergence between landlocked and anadromous populations is due to genetic drift in isolation because of a physical migration barrier. However, some reproductive isolating mechanism maintains genetic differentiation between sympatric populations in the Columbia River exhibiting alternative life history strategies (i.e. anadromous vs. ‘freshwater-type’). Non-native populations possessed genetic variants that were not observed in the species’ native range and were strongly differentiated from Atlantic Coast populations (\({\text{G}}^{{\prime }}_{\text{ST}}\)?=?0.218). Our results indicate that philopatry became established shortly after dispersal and colonization along the Pacific Coast. This study contributes to our understanding of dynamic evolutionary processes during invasions.     

Morphological differences between wild and farmed Mediterranean fish

Gilthead seabream (Sparus aurata L.) and European seabass (Dicentrarchus labrax L.) are important commercial marine fish species both for aquaculture and fisheries in the Mediterranean. It is known that farmed individuals escape from farm facilities, but the extent of escape events is not easy to report and estimate because of the difficulty to distinguish between wild and farmed individuals. In this study, significant differences provided through morphometry evidence that the cranial and body regions of seabream and seabass are different regarding their farm or wild origin at different scales. Morphological variations have been shown to be a valuable tool for describing changes in shape features. Therefore, the biomass contribution of escapees to local habitats could be determined by identifying escaped individuals from fisheries landings as a first step to assess the potential negative effects of fish farm escapees on the environment, and their influence on wild stocks and local fisheries.     

Northwest atlantic fisheries arrangements: A test of the species approach

Abstract

The United States government has advanced a proposal for a “species”; approach to the resolution of problems in the management and distribution of living marine resources. Under this approach, the management and distribution of the stocks of coastal species of fish would be handled by negotiation among interested parties on a stock‐by‐stock basis, with certain preferential rights accorded to the coastal state. This approach is now being tested in the developments taking place in the arrangements for the Northwest Atlantic fisheries. Here, IS nations agreed to divide up among themselves the annual yields of 14 separate stocks of fish. In addition, it has now been proposed that there be a limit on the total amount of fishing effort and a division of the total among states. The controls are based solely on the physical attributes of fishing and fail to take account of economic consequences. Because of this, questions can be raised about the viability of the arrangements and of the “species”; approach to the international law of fisheries.     

Population biology and the management of fisheries

The successful management and exploitation of fisheries requires detailed knowledge of the population dynamics and life histories of commercial species, and of the factors affecting recruitment and mortality. Much progress has been made in recent years, exemplified by the report of the 1984 Dahlem Workshop on the exploitation of marine communities, and by subsequent research discussed in this article. In some fisheries at least, management decisions can now have a firm scientific base.     

Conservation goals and fisheries management units for Atlantic salmon in the Baltic Sea area

The effective application of genetic information in fisheries management strategies implies political goal setting taking both conservation and fisheries management into account. The concept of sustainable use as set out by the Convention on Biological Diversity offers a valuable starting point in this respect, since the criterion for it is defined as the maintenance of genetic diversity within each species. However, strategic decisions are also needed on the practical level, where the actual genetic information can be taken into account. Genetic factors, such as glacial differentiation, the postglacial genetic structure of populations, gene flow levels and the probability of the existence of adaptive differences, have an effect on the formation of conservation and management units and on the long-term strategy for the sustainable use of aspecies. The Atlantic salmon ( Salmo salar ) in the Baltic Sea area is treated here as an example of a complicated management problem with a highly hierarchical genetic structure associated with marked loss of naturally reproductive stocks, extensive hatchery production and an effective international offshore fishery. The implications of genetic factors for the conservation and management strategy of the Baltic salmon is discussed in the light of the goals set by the Convention on Biological Diversity, the Straddling Fish Stocks and Highly Migratory Fish Stocks Agreement, the Habitats Directive of the European Union and the International Baltic Sea Fishery Commission.