Fishery Landings Research Articles

Productivity and Sustainable Management of the Humboldt Current Large Marine Ecosystem under climate change

The Humboldt Current Large Marine Ecosystem (HCLME) covers 95% of the southeast Pacific seaboard of which the area of influence from the Humboldt Current and associated upwelling areas in the Humboldt Current System (HCS) stretches from around 4° to 40° south. Global warming will likely affect marine circulation and land-atmosphere-ocean exchanges at the regional level, affecting the productivity and biodiversity patterns along the HCLME. The expected decrease of upwelling productivity in the HCS could be amplified by worldwide trends of oxygen depletion and lower pH. In addition, higher frequency of extreme climatic events, such as El Niño in a warmer ocean, might augment the risks for the recruitment success of anchovy and other short-lived fish resources, especially in the Northern HCLME. A range of non-climatic anthropogenic stressors also combines to reduce productivity and biomass yields. Transboundary Diagnostic Analysis (TDA) work has shown that overfishing and pollution are the main contributing factors in addition to the shared problem between Chile and Peru of high levels of fisheries bycatch and discards. An economic valuation of the HCLME and HCS has been finalized with an estimated annual delivery of around USD19.5 billion in goods and services. With many knowledge gaps this is evidently an underestimate but indicates which mitigating activities under a recently developed bi-national Strategic Action Programme (SAP) need to be prioritized. Fisheries landings are declining and demand for products is increasing. Improvement of ecosystem planning and management tools with value addition options for marine products is needed to adapt to climate change.

Size of catch, reproduction and feeding of the small-eye smooth-hound, <em>Mustelus higmani</em> (Carcharhiniformes: Triakidae), in Margarita Island, Venezuela

Mustelus higmani is categorized as “least concern” according to the red list of the International Union for Conservation of Nature, but gaps in population trends occur in most of its distribution range. In Venezuela, this species has local importance because it is part of typical dishes. The aim of this work is to analyse the population structure, reproduction and feeding of M. higmani from Margarita Island’s artisanal fishery landings for management purposes. Between 2006 and 2008, 2223 specimens were analysed: 1156 females (24.8-88.4 cm total length [TL]) and 1067 males (20-69.2 cm TL). Temporal variations in sex ratio and length class structure were detected. Changes in body size were detected throughout different years of sampling. A decrease in TL and an increase in immature specimens in the catch were observed in 2008. Mean length at maturity (L50) was estimated at 46.7 cm TL for females and 47.6 cm TL for males. Female fecundity was 4±1.8 embryos (n=388). Length at birth was between 20 and 29 cm TL, and no differences in sex ratio were detected for embryos. Feeding analyses (n=266 stomachs) showed a diet mainly based on decapod crustaceans, small fish, stomatopods and cephalopods. The trophic level was 3.3, which shows feeding based on benthic and demersal species of the continental shelf, especially crustaceans.

Indirect signals of spawning aggregations of three commercial reef fish species on the continental shelf of Bahia, east coast of Brazil

AbstractLutjanus analis (Mutton snapper), Lutjanus jocu(Dog snapper) and Mycteroperca bonaci (Black grouper) are reef fishes of high commercial value, and are among the principal exploited reef resources on the eastern and northeastern coast of Brazil. These species share the habit of forming transient spawning aggregations, predictable in time and space, which leaves them particularly vulnerable. The present study aimed to obtain indirect indicators of periods and places of spawning aggregations for these species, based on the exploratory analysis of available data on commercial catches and fishing efforts in Southern Bahia. Line fishery landings data were monitored in 12 locations in the region, and catch records of Mutton snapper (1320 landings), Dog snapper (654) and Black grouper (1162) were analyzed. A strategy was developed for exploratory analysis of monthly CPUE variation and individual distribution of CPUE per trip. The results showed the occurrence of aggregations in 26 specific sites, with values of relative abundance far above the annual mean, during spring/summer and autumn/winter. The occurrence of these anomalous catches was validated with the fishermen responsible for respective fishing trips. Additional studies are needed to confirm spawning activity at these sites. Analysis of inter-annual variation suggests a decreasing trend in relative abundance of Black grouper and Mutton snapper, possibly associated with unregulated fishing of spawning aggregations.

Productivity and biomass of fishes in the California Current Large Marine Ecosystem: Comparison of fishery-dependent and -independent time series

Commercial landings are often the only data available to assess the status of marine fish populations, but may reflect economics, technology and management policy in addition to stock size. In the California Current Large Marine Ecosystem (CCLME), the availability of CalCOFI ichthyoplankton data enabled us to compare commercial landings with a fishery-independent time series from 1951 to 2011. Fishery landings for the CCLME generally increased over this period, peaking about 1990 and displaying no clear subsequent trend. However, the abundance of ichthyoplankton in the southern CCLME has declined by ~70% since about 1970, based on the decline of taxa with cool-water affinities, apparently related to ocean warming and reduced productivity, and of mesopelagic taxa since the 1990s in response to declining midwater oxygen concentrations. These results highlight the importance of sustained fishery-independent time series at a time of secular climate change.Calibration of the larval fish abundance time series with stock assessments and acoustic/trawl surveys provided a proxy time series of spawning stock biomass for epi- and mesopelagic planktivores since 1951. We estimate that mesopelagic fishes comprised ~83% of the biomass of plankton-feeding fishes in the southern CCLME, but their prey consumption appears approximately equivalent to that of epipelagic planktivores because of the greater metabolic requirements of epipelagic fishes. The “wasp-waist” paradigm for eastern boundary currents needs to be re-assessed based on revised assessments for the abundance of mesopelagic fishes.

Spatial Analysis of the Abundance and Catchability of the Red OctopusOctopus maya(Voss and Solís-Ramírez, 1966) on the Continental Shelf of the Yucatan Peninsula, Mexico

The red octopus Octopus maya is an endemic species of the continental shelf of the Yucatan Peninsula, Mexico and supports the largest octopus fishery in the American continent. Little is, however, known about its spatial dynamics. The study of the space-time variation of catchability is a key element in the stock assessment, because it allows behavioral aspects of the resource and qualities of the various exploitation strategies to be clarified, which are essential for the fishery management. The objective was to analyze the spatio-temporal variations of the abundance and catchability of the octopus O. maya on the continental shelf of the Yucatan Peninsula, Mexico. During the fishing season of 2012 (August–December), fishery landings from the small-scale fleet in 13 ports of the Yucatan Peninsula, were analyzed to obtain data on catch, effort and fishing zone for O. maya. During the closed season of 2013 (January–July) fishing hauls were performed across a network of stations along the coast of the Yucatan Peninsula. Spatio-temporal variations in mean catch per unit effort (CPUE) in terms of number of organisms per hour of effective fishing were analyzed. Catchability and its variation with size, time, and zone were estimated through a model based on the Leslie transition matrix and frequency distributions of mantle length. The results showed significant changes in the distribution of O. maya. During the fishing season, the greatest abundances were found along the coast of Campeche (western zone), whereas, during the closed season the highest abundances were recorded along the coast of Yucatan (eastern zone). Trends of decreasing and increasing catchability were observed with respect to size according to the different zones. A high catchability was presented for small sizes along the coast of Campeche during the fishing season. The results indicate the need to investigate possible management measures differentiated by region (west-east) to ensure the fishery sustainability.

Impacts of fishing on the marine mean trophic level in Chinese marine area

Studying the long-term effects of fishing on the marine mean trophic level (MTL) is very important for understanding the status of marine ecosystems, and it will help in the design of appropriate conservation management strategies. Using data on fishery landings from the FAO Fishery Statistics (FishStatJ_2.0.0_win32, 1950 to 2011), we analyzed changes in the fishery landings of 51 marine species/groups in the Chinese marine area and their impacts on MTL. We obtained the following results: China's fishery landings increased gradually from 0.72×106t to 3.29×106t between 1950 and 1977; it increased sharply from 2.74×106t to 13.21×106t between 1981 and 1998, declined to 12.00×106t in 2002 and remained relatively stable until 2008, and increased again to 12.86×106t between 2009 and 2011. The percentage of landings from species/groups whose trophic level was higher than 3.5 was about 28% in 1975–1977; it declined to 17.1% in 1979–1981, increased to 27.00% in 1979–1981, declined from 24.57% to 13.64% in 1982–1988, fluctuated around 19.43% in 1997, and then increased steadily to 35.8% from 1997 to 2011. China's MTL remained stable from 1950 to 1974, fluctuated slightly around 3.45, declined to 3.35 in 1975–1978, and increased to 3.45 in 1979–1981. However, the MTL declined sharply to 3.25 in 1982–1987 and remained stable 10years afterwards. The decreasing rate of MTL was 0.05 per decade during 1950–1997; it increased gradually to 3.34 from 1997 to 2011, during which the increasing rate was 0.12 per decade. The fishing in balance index of Chinese marine area showed a clear increasing trend since 1950; the trend was greater than 0.5 since 1959, and it increased to greater than 1 since 1995. The changes in MTL were closely related to the composition of the fish species/groups in the total fishery landings, especially the fish species/groups of which the MTL was greater than 3.5, such as Trichiurus haumela, Larimichthys polyactis, Larimichthys crocea, Engraulis japonicas, and Decapterus spp. The general declining trend of MTL indicates that the dominant fishery landings changed from benthic fishes with a long life span and high trophic level (e.g., T. haumela) to invertebrates and pelagic fishes with a short life span and low trophic level (e.g., Decapterus spp.). The increase in MTL in China from 1997 to 2011 may be attributable to a series of fishery management countermeasures, such as setting up closed fishing seasons and non-fishing zones, establishing marine protected areas for fishery restoration. We also found that MTL may differ when statistical landings data and species richness data are used, and may be affected by the quality of the fisheries statistics. Moreover, species' trophic level, which is assumed to be constant, may have changed over time. The effects of these factors on MTL should be explored in the future.

A popular and potentially sustainable fishery resource under pressure–extinction risk and conservation of Brazilian Sciaenidae (Teleostei: Perciformes)

Croakers (Sciaenidae) are major fishery resource in Brazil; constituting 22% of marine and 9% of freshwater fishery landings. Croakers are subject to heavy fishing pressure throughout Brazil, but habitat alteration is also an important threat to regional populations. In this regional Sciaenidae assessment, each species was analyzed for relative risk of extinction, including the identification and quantification of the impact of major threats and existing conservation measures, based on application of the Categories and Criteria of the IUCN Red List of Threatened Species. Of the 52 species of Sciaenid fishes (34 marine and 18 freshwater) present in Brazilian waters, the majority are at low risk of extinction, with 10 species classified as Data Deficient (DD) and 36 as Least Concern (LC). However the Southern black drum (Pogonias cromis), listed as Endangered (EN) is the most threatened species in the region, while three other species are classified as Near Threatened (NT). A large portion of Brazilian croakers is landed by small-scale artisanal fisheries, which are scattered along coastal and riverine communities. However, our assessments reveal that available fishery landing statistics may have greatly underestimated the artisanal fishery production and by-catch of Sciaenids. We recommend establishing, with adequate enforcement, coastal and riverine protected areas as well as strategic fishing seasons to improve and maintain the conservation status of Sciaenids and sustainable Sciaenid fisheries.

Aspiring to an altered stable state: rebuilding of bay scallop populations and fisheries following intensive restoration

Intensive efforts to restore bay scallop Argopecten irradians irradians populations and fisheries in the Peconic Bays of eastern Long Island, New York, USA, were begun in 2006, fol- lowing a 12 yr period during which commercial fishery landings averaged 1 to 2% of historical levels seen prior to 1985 to 1995 brown tide algal blooms. Compared to 2005 to 2006, natural pop- ulation densities of 0+ yr scallops in fall increased 16 × by 2007 in Orient Harbor (OH), the focus of our restoration efforts; by 2009, densities in OH and other, unplanted, embayments had increased by 110 × and up to 331 ×, respectively. Spatial and temporal patterns paralleled those documented for larval recruitment; highly significant correlations between commercial harvest levels and both baywide larval settlement and juvenile benthic densities were revealed. Official fishery landings were 13 × those of pre-restoration levels by 2010 and have remained relatively stable through 2013. Following commencement of restoration, dockside revenues and economic benefit to the regional economy have increased by ~US$2 million and $20 million, respectively; our calculations suggest that these figures are 40% of actual numbers. Population resurgence is not correlated to temporal changes in predator populations or submerged aquatic vegetation cover. We conclude that rebuilding of Peconic bay scallop populations and fisheries has been driven by dramatic increases in bay scallop larval supply emanating from our intensive restoration efforts. By defini- tion, we cannot say that Peconic bay scallops have attained an alternate stable state, but it is clear that dramatic increases in populations, fishery landings, and economic value are possible in just a few years.

Spatial analyses reveal conservation benefits for cold-water corals and sponges from small changes in a trawl fishery footprint

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 528:161-172 (2015) - DOI: https://doi.org/10.3354/meps11271 Spatial analyses reveal conservation benefits for cold-water corals and sponges from small changes in a trawl fishery footprint Cory R. Lagasse1,*, Anders Knudby2, Janelle Curtis3, Jessica L. Finney3, Sean P. Cox1 1School of Resource and Environmental Management, and 2Department of Geography, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada 3Pacific Biological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Rd., Nanaimo, British Columbia V9T 6N7, Canada *Corresponding author: clagasse@sfu.ca ABSTRACT: Spatial closures are an important component of regulations to protect cold-water corals and sponges from potential damage by bottom trawling. However, designing spatial closures can be challenging because the distribution of most cold-water coral and sponge habitat is unknown, and closures that overlap with fishing areas may reduce fishing opportunities and landings. In this paper, we examined trade-off relationships between bottom trawl fishery landings and the proportion of coral and sponge habitat protected by alternative spatial closure designs within Hecate Strait, British Columbia, Canada. We selected closures using a spatial optimization procedure involving 3 steps: (1) maximum entropy species distribution modelling to predict habitat suitability for Hexactinellida sponges and Alcyonacea and Pennatulacea corals, (2) matching habitat suitability predictions with spatially explicit estimates of bottom trawl landings value from at-sea observer data, and (3) Marxan spatial optimization to select closures that protect the most suitable coral and sponge habitat while minimizing losses in landings value. Our results suggest that the majority of coral and sponge habitat within Hecate Strait could be protected while maintaining existing fisheries value; spatial closures protecting up to 70% of the most suitable coral and sponge habitat resulted in negligible losses in trawl fishery landings. Protecting 99% of suitable coral and sponge habitats decreased landings value to 63% of its former total. Landings for rockfishes Sebastes and Sebastolobus spp. were the most sensitive to spatial closures, decreasing twice as much as average landings value for all groundfish species. By explicitly revealing potential trade-offs between fisheries and conservation objectives, our analysis provides a concrete starting point towards implementing spatial closures with increased transparency, credibility, and acceptability from stakeholders. KEY WORDS: Bottom trawling · Cold-water corals and sponges · Conservation planning · Marxan · Maximum entropy · Species distribution modelling · Trade-offs Full text in pdf format Supplementary material PreviousNextCite this article as: Lagasse CR, Knudby A, Curtis J, Finney JL, Cox SP (2015) Spatial analyses reveal conservation benefits for cold-water corals and sponges from small changes in a trawl fishery footprint. Mar Ecol Prog Ser 528:161-172. https://doi.org/10.3354/meps11271 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 528. Online publication date: May 28, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Temporal and spatial availability of Atlantic Thread Herring, Opisthonema oglinum, in relation to oceanographic drivers and fishery landings on the Florida Panhandle

AbstractSince 1995, landings of Atlantic Thread Herring (Opisthonema oglinum) on the Florida Panhandle averaged 124 mt each spring (April–June) but declined to nearly zero in 1996–97 and 2006. To elucidate causes of recurring periods of low landings, we used generalized additive mixed models (GAMMs) to examine the relationship between Atlantic Thread Herring catch in a trawl survey on the west‐central coast of Florida and four environmental variables. Chlorophyll‐a was significant in the models, indicating a direct relationship between local abundance of baitfish and their planktonic food. Temperature and depth were also significant whereas salinity was not. During 2003 and 2012, synoptic satellite‐derived temperature and chlorophyll‐a maps were used with the GAMMs to predict monthly spatial availability on the Florida Panhandle fishing grounds (long. 85–88o W and depth 12–25 m). The predicted monthly availability was significantly correlated with commercial catch rates (Pearson's r = 0.26, P = 0.004, d.f. = 118). We used multiple linear regression (MLR) with lags to describe the effect of river discharge and wind (as a transport mechanism) on surface chlorophyll‐a over the Panhandle fishing grounds. Discharge from local rivers was significant in all MLRs, and the Mississippi was only significant as an interaction with wind. We conclude that Atlantic Thread Herring are distributed over the Panhandle fishing grounds based on food availability that is driven by river discharge and eastward transport of Mississippi River plumes. This analysis improves our understating of baitfish dynamics, an important ecosystem component in the Gulf of Mexico.

Environmental influence on commercial fishery landings of small pelagic fish in Portugal

Small pelagic fishes are particularly abundant in areas with high environmental variability (zones of coastal upwelling and areas of tidal mixing and river discharge), and because of this, their abundance suffers large inter-annual and inter-decadal fluctuations. In Portugal, the most important species in terms of landings are European sardine, Atlantic horse mackerel and Atlantic chub mackerel. Small pelagic fish landings account for 62.8 % of the total fish biomass and represent 32.7 % of the economical value of all catches. We have investigated trends in landings of these small pelagic fishes and detected the effects of environmental factors in this fishery. In order to explain the variability of landings of small pelagic fishes, we have used official landings (1965–2012) for trawling and purse seine fisheries and applied generalized linear models, using the North Atlantic Oscillation index (NAO) (annual and winter NAO index), sea surface temperature (SST), wind data (strength and North–South and East–West wind components) and rainfall, as explanatory variables. Regression analysis was used to describe the relationship between landings and SST. The models explained between 50.16 and 51.07 % of the variability of the LPUE, with the most important factors being winter NAO index, SST and wind strength. The LPUE of European sardine and Atlantic horse mackerel was negatively correlated with SST, and LPUE of Atlantic chub mackerel was positively correlated with SST. The use of landings of three important species of small pelagic fishes allowed the detection of variations in landings associated with changes in sea water temperature and NAO index.

Evidence of climate-driven ecosystem reorganization in the Gulf of Mexico.

The Gulf of Mexico is one of the most ecologically and economically valuable marine ecosystems in the world and is affected by a variety of natural and anthropogenic phenomena including climate, hurricanes, coastal development, agricultural runoff, oil spills, and fishing. These complex and interacting stressors, together with the highly dynamic nature of this ecosystem, present challenges for the effective management of its resources. We analyze a compilation of over 100 indicators representing physical, biological, and economic aspects of the Gulf of Mexico and find that an ecosystem-wide reorganization occurred in the mid-1990s. Further analysis of fishery landings composition data indicates a major shift in the late 1970s coincident with the advent of US national fisheries management policy, as well as significant shifts in the mid-1960s and the mid-1990s. These latter shifts are aligned temporally with changes in a major climate mode in the Atlantic Ocean: the Atlantic Multidecadal Oscillation (AMO). We provide an explanation for how the AMO may drive physical changes in the Gulf of Mexico, thus altering higher-level ecosystem dynamics. The hypotheses presented here should provide focus for further targeted studies, particularly in regard to whether and how management should adjust to different climate regimes or states of nature. Our study highlights the challenges in understanding the effects of climatic drivers against a background of multiple anthropogenic pressures, particularly in a system where these forces interact in complex and nonlinear ways.

Consumption by marine mammals on the Northeast U.S. continental shelf

The economic and ecological impacts of fish consumption by marine mammals, the associated interactions with commercial fish stocks, and the forage demands of these marine mammal populations are largely unknown. Consumption estimates are often either data deficient or not fully evaluated in a rigorous, quantitative manner. Although consumption estimates exist for the Northeast United States (NEUS) Large Marine Ecosystem, there is considerable uncertainty in those estimates. We examined consumption estimates for 12 marine mammal species inhabiting the regional ecosystem. We used sensitivity analyses to examine metabolically driven daily individual consumption rates, resulting in a suite of feasible parameter-pair ranges for each of three taxonomic groups: mysticetes, odontocetes, and pinnipeds. We expanded daily individual consumption to annual consumption based on abundance estimates of marine mammals found on the NEUS continental shelf coupled with estimates of annual residence time for each species. To examine consumptive removals for specific prey, diet compositions were summarized into major prey categories, and predatory removals by marine mammal species as well as for total marine mammal consumption were estimated for each prey taxa. Bounds on consumption estimates for each marine mammal species were determined using Monte Carlo resampling simulations. Our results suggest that consumption for these 12 marine mammal species combined may be similar in magnitude to commercial fishery landings for small pelagic and groundfish prey groups. Consumption by marine mammals warrants consideration both as a source of mortality in assessments of prey-stocks, and to determine marine mammal forage demands in ecosystem assessment models. The approach that we present represents a rigorous, quantitative method to scope the bounds of the biomass that marine mammals are expected to consume, and is appropriate for use in other ecosystems where the interaction between marine mammals and commercial fisheries is thought to be prominent.

PCR–RFLP analysis to identify four ray species of the genus Dasyatis (Elasmobranchii, Dasyatidae) fished along the southeastern and southern coast of Brazil

Fisheries statistics and stock assessment of many species of rays have been limited by the lack of information at the species level. Given the difficulty in identifying the four species within genus Dasyatis found in southeastern and southern Brazil, the aim of this work was to develop a methodology based on polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) of the mitochondrial cytochrome oxidase I (COI) gene to distinguish and register the capture frequencies of these species. Amplification of the COI region was performed using universal fish R1 and F2 primers, which generated amplicons of approximately 650bp that subsequently were sequenced. The FokI restriction enzyme was selected and generated specific DNA fragments for each species, with two fragments for Dasyatis hypostigma (390 and 260bp), three fragments for Dasyatis americana (300, 180 and 155bp), two fragments for Dasyatis guttata (370 and 300bp), and two fragments for Dasyatis centroura (410 and 200bp). The same enzyme then was used to identify 97 samples of ray carcass tissues collected from fishery landings, and revealed a species occurrence of 90.7% for D. hypostigma, 5.1% for D. americana, 2.1% for D. guttata, and 2.1% for D. centroura. Thus, the PCR–RFLP technique can be used to efficiently identify these four species and serves as an indicator of the current catch rates. Moreover, the method can help solve misidentification problems and can be used routinely to monitor landings and to establish and implement plans for fishery management.

Use of a seagrass residency index to apportion commercial fishery landing values and recreation fisheries expenditure to seagrass habitat service.

Where they dominate coastlines, seagrass beds are thought to have a fundamental role in maintaining populations of exploited species. Thus, Mediterranean seagrass beds are afforded protection, yet no attempt to determine the contribution of these areas to both commercial fisheries landings and recreational fisheries expenditure has been made. There is evidence that seagrass extent continues to decline, but there is little understanding of the potential impacts of this decline. We used a seagrass residency index, that was trait and evidence based, to estimate the proportion of Mediterranean commercial fishery landings values and recreation fisheries total expenditure that can be attributed to seagrass during different life stages. The index was calculated as a weighted sum of the averages of the estimated residence time in seagrass (compared with other habitats) at each life stage of the fishery species found in seagrass. Seagrass-associated species were estimated to contribute 30%-40% to the value of commercial fisheries landings and approximately 29% to recreational fisheries expenditure. These species predominantly rely on seagrass to survive juvenile stages. Seagrass beds had an estimated direct annual contribution during residency of €58-91 million (4% of commercial landing values) and €112 million (6% of recreation expenditure) to commercial and recreational fisheries, respectively, despite covering <2% of the area. These results suggest there is a clear cost of seagrass degradation associated with ineffective management of seagrass beds and that policy to manage both fisheries and seagrass beds should take into account the socioeconomic implications of seagrass loss to recreational and commercial fisheries.

Dynamic hypoxic zones in Lake Erie compress fish habitat, altering vulnerability to fishing gears

Seasonal degradation of aquatic habitats from hypoxia occurs in numerous freshwater and coastal marine systems and can result in direct mortality or displacement of fish. Yet, fishery landings from these systems are frequently unresponsive to changes in the severity and extent of hypoxia, and population-scale effects have been difficult to measure except in extreme hypoxic conditions with hypoxia-sensitive species. We investigated fine-scale temporal and spatial variability in dissolved oxygen in Lake Erie as it related to fish distribution and catch efficiencies of both active (bottom trawls) and passive (trap nets) fishing gears. Temperature and dissolved oxygen loggers placed near the edge of the hypolimnion exhibited much higher than expected variability. Hypoxic episodes of variable durations were frequently punctuated by periods of normoxia, consistent with high-frequency internal waves. High-resolution interpolations of water quality and hydroacoustic surveys suggest that fish habitat is compressed during hypoxic episodes, resulting in higher fish densities near the edges of hypoxia. At fixed locations with passive commercial fishing gear, catches with the highest values occurred when bottom waters were hypoxic for intermediate proportions of time. Proximity to hypoxia explained significant variation in bottom trawl catches, with higher catch rates near the edge of hypoxia. These results emphasize how hypoxia may elevate catch rates in various types of fishing gears, leading to a lack of association between indices of hypoxia and fishery landings. Increased catch rates of fish at the edges of hypoxia have important implications for stock assessment models that assume catchability is spatially homogeneous.

Estimating the Sex Composition of the Summer Flounder Catch using Fishery‐Independent Data

AbstractModels that account for sex‐specific behavior and population dynamics are becoming more common in the stock assessment of sexually dimorphic fishes. However, such models can be data intensive and require some knowledge or assumptions about the sex ratio of fishery landings. A recent stock assessment review of Summer Flounder Paralichthys dentatus identified the need to account for sex‐specific fishing mortality in the assessment model; however, no data on the sex composition of the catch were available. Fishery‐independent, sex‐specific information for this species is collected annually by the National Marine Fisheries Service's Northeast Fisheries Science Center during their bottom trawl survey. Sex at age from the survey could be applied to the fishery landings if the probability of landing a given sex at a given age is equivalent for fish collected by the survey and those in the landings. To generate the first regionally comprehensive database on the sex ratio of Summer Flounder landings and to determine the efficacy of using survey sex‐at‐age keys to estimate the sex of landed fish, we recorded the sex composition of the commercial and recreational catches of Summer Flounder (n = 31,912) in 2010 and 2011. When (1) trawl survey length data were left‐truncated to simulate the minimum retention sizes in the fisheries and (2) age–length keys generated from fishery‐dependent data were applied to length frequency distributions from the survey to simulate the growth rates of landed fish, the sex‐at‐age pattern in the survey‐derived data closely resembled the patterns in the catch. However, statistically significant differences in sex at age remained between the catch and the survey‐derived data. We hypothesize that these differences are attributable to differences in the spatiotemporal distributions of the sexes and of the survey and fishing effort.Received March 9, 2015; accepted June 23, 2015

The Response of Fish Communities to Climate and Human-Induced Changes Inferred from Fishery Landings in an Enclosed Bay

Variations in the fish community structure in Omura Bay, an enclosed bay in the East China Sea, were investigated using long-term fishery landing data over the past five decades (1965–2006). We confirmed that the fish community structure in Omura Bay showed three conspicuous regimes during the study period. Anchovies dominated in the pelagic domain with abundant and various demersal fish species in the first phase (1965–1978). Demersal fish declined remarkably with the dominance of sardines in the pelagic domain during the second phase (1979–1987), and the fish community was simplified with the return of anchovies and no recovery of demersal fish in the third phase (1988–2006). These changes were significantly related with periodic large-scale climate changes and cumulative regional-scale human impacts. The replacement of sardine/anchovy caused by a climate regime shift in the North Pacific contributed to the fish community regime shifts in Omura Bay. Moreover, habitat degradation such as depletion of dissolved oxygen combined with climate-induced changes in food web systems resulted in a rapid reduction in demersal fish. Contraction of the habitat volume due to an increase in oxygen-restricted water simplified the fish community structure and eventually reduced fishery landings in Omura Bay. These findings demonstrate that long-term fish community responses to large-scale climate changes and regional-scale human impacts can be observed in a coastal enclosed bay, providing useful information for fisheries management in areas with climate and human-induced changes.

Overfishing and the replacement of demersal finfish by shellfish: an example from the English Channel.

The worldwide depletion of major fish stocks through intensive industrial fishing is thought to have profoundly altered the trophic structure of marine ecosystems. Here we assess changes in the trophic structure of the English Channel marine ecosystem using a 90-year time-series (1920–2010) of commercial fishery landings. Our analysis was based on estimates of the mean trophic level (mTL) of annual landings and the Fishing-in-Balance index (FiB). Food webs of the Channel ecosystem have been altered, as shown by a significant decline in the mTL of fishery landings whilst increases in the FiB index suggest increased fishing effort and fishery expansion. Large, high trophic level species (e.g. spurdog, cod, ling) have been increasingly replaced by smaller, low trophic level fish (e.g. small spotted catsharks) and invertebrates (e.g. scallops, crabs and lobster). Declining trophic levels in fisheries catches have occurred worldwide, with fish catches progressively being replaced by invertebrates. We argue that a network of fisheries closures would help rebalance the trophic status of the Channel and allow regeneration of marine ecosystems.

Modelling the effects of climate change on a Caribbean coral reef food web

Global climate change and local anthropogenic pressures are among the primary factors leading to the decline of functional biodiversity and critical habitats in coral reefs. Coral bleaching, the potential decreases in dissolved oxygen concentration (deoxygenation) and pH (acidification) in the oceans can induce severe changes in coral reef ecosystem biodiversity and functionality. The main objective of this study was to apply four Ecopath with Ecosim models of a Caribbean coral reef system to individually and collectively model the effects of coral bleaching on the trophic web, deoxygenation on fish, and acidification on calcifying organisms. These three sources of stress were used as forcing functions on several trophic groups depending on the model. The forcing functions were scaled according to the species’ responses achieved in previously tested climate change marine models. For the bleaching model, a mediation function was also considered that represents the degree of coral reef protection on small and intermediate fish groups. The dynamic models were constructed from an extensive database of 171 reef fish species (abundance and biomass) and benthic communities from 13 coral reefs that were evenly distributed parallel to approximately 400km of the Mexican Caribbean coast as well as fishery landings in this area. Simulations driven with these different forcing and mediation functions predicted different changes in the biomasses of fish and non-fish functional groups as well as the biomass of the functional groups of fished species. Coral bleaching and pH reduction caused a phase shift to a decrease in coral biomass and an increase in primary producer biomass. This shift produced a cascading decrease in the biomass of small and intermediate fish groups. Additionally, the fished functional group biomass increased with coral bleaching but decreased with the effects of decreased oxygen on fish and pH on calcifying organisms. The biomasses of certain macroinvertebrate functional groups were predicted to respond favourably to the combined effect of the sources of stress. However, when all the sources of stress were combined, we found a general decrease of biomass in fish, non-fish, and some commercially valuable fish and macroinvertebrate functional groups, suggesting that the combined effects of stress induced synergistic effects as a result of global climate change and overfishing, which can result in a potential loss of biodiversity and ecosystem services in coral reefs.