Variation In Catch Research Articles

Environmental Factors Affecting the Daily Catch Levels ofAnguilla japonicaGlass Eels in the Geum River Estuary, South Korea

Hwang, S.D.; Lee, T.W.; Choi, I.S., and Hwang, S.W., 2014. Environmental factors affecting the daily catch levels of Anguilla japonica glass eels in the Geum River estuary, South Korea.The Japanese eel, Anguilla japonica, is a catadromous fish whose recruitment stage glass eels enter estuaries and rivers after being born offshore in the ocean. The daily variation in glass eel catch was analyzed in relation to environmental factors that affect upstream migration. The first glass eels of the 2003 season were caught in the Geum River estuary in early March, when the water temperature exceeded 5°C. The catch rates peaked in mid-March, when the temperature reached 6–7°C. Few glass eels were caught when the temperature was above 14–16°C in early May. Water temperature may have triggered the timing of glass eel immigration. The catch fluctuated with tidal cycle, since the catch level was relatively high during each new and full moon throughout the sampling period. A generalized additive model indicated that the glass eel catch was significantly related to tidal range, temperature, and salinity. To estimate the effect of minor factors, such as salinity and wind speed, on catch rate, we calculated the standardized residuals of catch rate. The standardized residuals of catch rate did not show any correlations to freshwater inflow or cloud cover, but occasionally increases were seen as a result of drops in salinity and 2–3 days after strong winds, suggesting that these factors may also trigger upstream migration of glass eels in the estuary.

Evaluation of three harvest control rules for Bigeye Tuna (Thunnus obesus) fisheries in the Indian Ocean

The stock of Bigeye tuna (Thunnus obesus) in the Indian Ocean supports an important international fishery and is considered to be fully exploited. The responsible management agency, the Indian Ocean Tuna Commission (IOTC), does not have an explicit management decision-making framework in place to prevent over-fishing. In this study, we evaluated three harvest control rules, i) constant fishing mortality (CF), from 0.2 to 0.6, ii) constant catch (CC), from 60000 to 140000 t, and iii) constant escapement (CE), from 0.3 to 0.7. The population dynamics simulated by the operating model was based on the most recent stock assessment using Stock Synthesis version III (SS3). Three simulation scenarios (low, medium and high productivity) were designed to cover possible uncertainty in the stock assessment and biological parameters. Performances of three harvest control rules were compared on the basis of three management objectives (over 3, 10 and 25 years): i) the probability of maintaining spawning stock biomass above a level that can sustain maximum sustainable yield (MSY) on average, ii) the probability of achieving average catches between 0.8 MSY and 1.0 MSY, and iii) inter-annual variability in catches. The constant escapement strategy (CE=0.5), constant fishing mortality strategy (F=0.4) and constant catch (CC=80000) were the most rational among the respective management scenarios. It is concluded that the short-term annual catch is suggested at 80000 t, and the potential total allowable catch for a stable yield could be set at 120000 t once the stock had recovered successfully. All the strategies considered in this study to achieve a ‘tolerable’ balance between resource conservation and utilization have been based around the management objectives of the IOTC.

Global Modular Principal Component Analysis

Modular Principal Component Analysis (ModPCA) divides a pattern into sub-patterns and extracts local Principal Components (PCs) from the sub-patterns. It is aimed to discriminate patterns better, as compared to PCA, by exploiting local variations that are confined to sub-patterns or sub-images. In contrast to ModPCA, PCA based classification does well by extracting trends global to the patterns and exhibits superior dimensionality reduction as compared to ModPCA. It is observed that, ModPCA which performs partitioning, does not catch variations spread across sub-patterns. As a result, when compared to PCA, it shows lower dimensionality reduction and consequently does not yield better classification when such global variations are widespread in the data. Now, it is crucial to exploit both local and global variations for better classification and dimensionality reduction. To overcome these issues of global PCA and local ModPCA methods, we bring-in a novel hybrid method which extracts PCs with global and local properties. Empirical results on standard UCI and face data confirm the higher dimensionality reduction of the proposed method over ModPCA, and improved overall classification against PCA and ModPCA methods. The proposed method is also proved to be robust in terms of classification over ModPCA with a variety of partitions.

Using model simulations to compare performance of two commercial salmon management strategies in Bristol Bay, Alaska

In this paper, we discuss the costs and benefits, in relation to economics and Alaska’s salmon management policies, associated with two management strategies on the Egegik and Togiak sockeye salmon (Oncorhynchus nerka) fisheries in Bristol Bay, Alaska. “Daily management” allows managers to open or close the fishery on a daily basis, whereas a fixed fishing schedule allows fishing, to the extent practical, on fixed days of the week. To compare the strategies, we simulated the effects of daily management and a fixed fishing schedule on the two fisheries. Our simulations show that a daily management strategy results in higher yearly catches, less yearly variation in escapement, and fewer years of escapement below the goal range. A fixed fishing schedule results in less yearly variation in catch and a more stable harvest rate, with the harvest stability more pronounced when effort was held constant. Daily management is a desirable strategy for fisheries that are managed for maximum sustainable yield, have high fishing effort, have a small fishing area, or have a more temporally compressed run. A fixed fishing schedule is a desirable strategy for fisheries with less intense effort, budgetary or efficiency concerns, or stock components that differ in run timing.

Cohort resonance: a significant component of fluctuations in recruitment, egg production, and catch of fished populations

Abstract Hjort (1914. Fluctuations in the great fisheries of northern Europe. Rapport et Procès-Verbaux des Réunions du Conseil Permanent International pour l'exploration de la Mer, XX: 1–228) identified two important aspects of the early life of fish as being important determinants of fluctuations in year-class strength: changes in nutrition and transport. He dismissed a third possible influence, changes in the abundance of the reproductive stock. Here, we describe how a recently discovered characteristic behaviour of age-structured populations termed cohort resonance, which does involve changes in adult abundance, can have a substantial effect on fluctuations in fished populations. Cohort resonance involves selectively greater sensitivity of age-structured populations to generational frequencies and to very low frequencies in the environmental signal influencing a population. This frequency-dependent selectivity has been shown to increase with fishing, as do the total amounts of variability in recruitment, egg production, and catch. Cohort resonance differs from other recent model mechanisms proposed to explain the observed increase in variability with fishing in that it does not require over-compensatory density-dependence. It stems from the compensatory ascending limb of the egg–recruit relationship, and is a characteristic of a stable population driven by a random environment. We demonstrate the differences in frequency selectivity and increases in variability with fishing among three different Pacific coast species with different longevity: coho salmon (Oncorhynchus kisutch; ∼3 years), Pacific hake (Merluccius productus; ∼25 years), and Pacific Ocean perch (Sebastes alutus; ∼90 years). The shortest lived, coho salmon is the most sensitive to environmental variability, but variability in egg production and catch both increase more rapidly with fishing in the longer-lived species. Understanding cohort resonance will aid in anticipation of predicted potential changes in the frequency content of the physical environment with changing climate (e.g. more frequent El Niños), and it provides a warning regarding the possible confounding of increasing sensitivity to slow change due to fishing with actual slow change of population parameters due to climate change. Our understanding of the role of cohort resonance in population variability will be enhanced by further identification of empirical examples. We describe some of the challenges in this effort.

Environmental and fishing effects on the dynamics of brown tiger prawn (Penaeus esculentus) in Moreton Bay (Australia)

This analysis of the variations of brown tiger prawn (Penaeus esculentus) catch in Moreton Bay multispecies trawl fishery estimated catchability using a delay difference model. It integrated several factors responsible for variations in catchability: targeting of fishing effort, increasing fishing power and changing availability. An analysis of covariance was used to define fishing events targeted at brown tiger prawns. A general linear model estimated inter-annual variations of fishing power. Temperature-induced changes in prawn behaviour played an important role on the dynamics of this fishery. Maximum likelihood estimates of targeted catchability (4.09±0.42×10−4boat-day−1) were twice as large as non-targeted catchability (1.86±0.25×10−4boat-day−1). The causes of recent declines in fishing effort in this fishery were discussed.

Distribution of demersal fishes along the US west coast (Canada to Mexico) in relation to spatial fishing closures (2003-2011)

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 501:169-190 (2014) - DOI: https://doi.org/10.3354/meps10674 Distribution of demersal fishes along the US west coast (Canada to Mexico) in relation to spatial fishing closures (2003-2011) Aimee A. Keller1,*, W. Waldo Wakefield2, Curt E. Whitmire2, Beth H. Horness1, Marlene A. Bellman1, Keith L. Bosley2 1Fishery Resource Analysis and Monitoring Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 2725 Montlake Boulevard East, Seattle, Washington 98112, USA 2Fishery Resource Analysis and Monitoring Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanographic and Atmospheric Administration, 2032 S. OSU Drive, Newport, Oregon 97365, USA *Corresponding author: aimee.keller@noaa.gov ABSTRACT: A temporally and spatially variable Rockfish Conservation Area (RCA) was established as a marine protected area along the US west coast in 2002 to protect stocks of rockfishes Sebastes spp. Since the RCA falls within the region sampled annually by the West Coast Groundfish Bottom Trawl Survey, we utilized data collected from 2003 to 2011 to evaluate whether establishment of the RCA influenced catch per unit effort (CPUE), species richness, and size distribution of demersal fishes. We compared CPUE and species richness among 3 management areas (continuously closed, periodically closed, and open to commercial bottom trawling) using analysis of covariance models that account for variability due to area, year, and depth. The most appropriate models for CPUE (35 species treated individually and aggregated into 6 subgroups) and species richness were selected using Akaike’s information criterion. All of the best-fit models were highly significant (p < 0.0001), explaining 3 to 76% of the variation in catch. For 27 species and 5 subgroups, mean CPUE was significantly greater within the area continuously closed to commercial bottom trawling relative to areas periodically closed or open. The most appropriate model for richness included area and year, and mean richness was greatest in the area continuously closed to trawling. Species-specific length composition distributions were calculated from subsampled individual lengths for 31 species. Significant differences in length frequency distributions were observed, with a higher proportion (~65%) of larger fish most often present in areas continuously closed to commercial bottom trawling (20 of 31 species) relative to other areas. Our data suggest that the RCA is an effective management tool for conserving not only rockfishes, but also other demersal fish species. KEY WORDS: California Current System · Demersal fishes · Spatial fisheries management · Rockfish Conservation Area Full text in pdf format PreviousNextCite this article as: Keller AA, Wakefield WW, Whitmire CE, Horness BH, Bellman MA, Bosley KL (2014) Distribution of demersal fishes along the US west coast (Canada to Mexico) in relation to spatial fishing closures (2003-2011). Mar Ecol Prog Ser 501:169-190. https://doi.org/10.3354/meps10674 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 501. Online publication date: March 31, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Yield and catch changes in a Mediterranean small tuna trap: a warming change effect?

AbstractSince the 17th century, the Tonnarella of Camogli, a small tuna trap, has been used to catch pelagic fish along the western coast of the Portofino Promontory (Ligurian Sea, Northwestern Mediterranean). The availability of long‐term datasets on fish yields (1950–1974 and 1996–2011), with information related to the seawater temperatures and the North Atlantic Oscillation (NAO), has allowed us to study the qualitative and quantitative changes in fish yields in the last decade and the possible relationships with the seasonal anomalies of temperature that have occurred in the Ligurian Sea. In 1950–1974, yields remained relatively constant over time (average of 35.6 ± 8.7 t·year−1). From 1996 through 2011, yields were high (42.9 ± 15.9 t·year−1) but inconsistent with strong annual variability in catches. The primary catches are Seriola dumerili, Auxis rochei, Trachurus spp. and Sarda sarda. Changes in species composition have occurred as well: S. dumerili, Sardinella sp. and Belone belone have appeared recently. Moreover, a significant decrease in the boreal scombroid (Scomber scombrus) and an increase of warm‐temperate carangids and other typically Southern Mediterranean species such as Coryphaena hippurus and Sphyraena viridensis, appear to be linked to the warming of the surface water layer, particularly evident in the Ligurian Sea, for the last 10 years. The analysis of this kind of trend may be a powerful tool for assessing structural changes of the pelagic fish community in the Ligurian Sea (Northwestern Mediterranean).

Angler effort and catch within a spatially complex system of small lakes

Spatial layout of waterbodies and waterbody size can affect a creel clerk’s ability to intercept anglers for interviews and to accurately count anglers, which will affect the accuracy and precision of estimates of effort and catch. This study aimed to quantify angling effort and catch across a spatially complex system of 19 small (<100ha) lakes, the Fremont lakes. Total (±SE) angling effort (hours) on individual lakes ranged from 0 (0) to 7,137 (305). Bank anglers utilized 18 of the 19 lakes, and their mean (±SE) trip lengths (hours) ranged from 0.80 (0.31) to 7.75 (6.75), depending on the waterbody. In contrast, boat anglers utilized 14 of the 19 lakes, and their trip lengths ranged from 1.39 (0.24) to 4.25 (0.71), depending on the waterbody. The most sought fishes, as indexed by number of lakes on which effort was exerted, were anything (17 of 19 lakes), largemouth bass Micropterus salmoides (15 of 19 lakes), and channel catfish Ictalurus punctatus (13 of 19 lakes). Bluegill Lepomis machrochirus, crappie Pomoxis spp., and largemouth bass were caught most frequently across the lakes, but catch rates varied considerably by lake. Of the 1,138 parties interviewed, most parties (93%) visited a single lake but there were 77 (7%) parties that indicated that they had visited multiple lakes during a single day. The contingent of parties that visited more than one lake a day were primarily (87%) bank anglers.. The number of lake-to-lake connections made by anglers visiting more than one waterbody during a single day was related to catch rates and total angling effort. The greater resolution that was achieved with a lake specific creel survey at Fremont lakes revealed a system of lakes with a large degree of spatial variation in angler effort and catch that would be missed by a coarser, system-wide survey that did not differentiate individual lakes.

Spatial management of Indian Ocean tropical tuna fisheries: potential and perspectives

Abstract Effective use of spatial management in the pelagic realm presents special challenges due to high fish and fisher mobility, limited knowledge and significant governance challenges. The tropical Indian Ocean provides an ideal case study for testing our ability to apply existing data sources to assessing impacts of spatial management on tuna fisheries because of several recent controversial spatial closures. We review the scientific underpinnings of pelagic MPA effects, spatio-temporal patterns of Indian Ocean tuna catch, bycatch and fish movements, and the consequences of these for the efficacy of spatial management for Indian Ocean tropical tuna fisheries. The tropical Indian Ocean is characterized by strong environmental fluctuations, regular seasonal variability in catch, large observed tuna displacement distances, relatively uniform catch-per-unit-effort and bycatch rates over space, and high fisher mobility, all of which suggest significant variability and movement in tropical tuna fisheries that are simply not well adapted to static spatial closures. One possible exception to this overall conclusion would be a large time/area closure east of Somalia. If closed for a significant fraction of the year it could reduce purse-seine bycatch and juvenile tuna catch. Dynamic closures following fish migratory patterns are possible, but more focused information on fish movements will be needed for effective implementation. Fortunately, several recent improvements in conventional fishery management and reporting will likely enhance our ability to evaluate spatial and non-spatial management options in the near future, particularly as pertaining to bycatch species.

Evaluating the Performance of Two Salmon Management Strategies using Run Reconstruction

AbstractCommercial salmon fisheries in Alaska are managed to obtain escapement goals within a fixed range while attempting to maximize sustained yield. Two management strategies currently being used are emergency order authority and a fixed fishing schedule. We analyzed and compared the historical performance of these two management strategies for Bristol Bay, Alaska, fisheries targeting Egegik River and Togiak River Sockeye Salmon Oncorhynchus nerka. To accomplish this, we reconstructed the daily runs to each river through the use of catch, effort, and tower count data. Our results showed that management by emergency order openings resulted in (1) the catch of a higher percentage of returning fish, (2) less yearly variation in escapement, and (3) escapements that were always above the minimum escapement goal. A fixed fishing schedule resulted in less yearly variation in catch and a harvest rate that was spread more evenly throughout the run; the more even harvest rate likely provides better protection of substocks and the sex ratio. Emergency order authority gives a manager greater control over the fishery but requires more informative data. A fixed fishing schedule provides a more predictable catch but carries a higher risk of overharvest. Each of the two management strategies was successful and was suited to the circumstances of its fishery.Received December 7, 2012; accepted September 13, 2013Published online February 10, 2014

A comparison of two gears for quantifying abundance of lotic-dwelling crayfish

Crayfish (saddlebacked crayfish, Orconectes medius) catch was compared using a kick seine applied two different ways with a 1-m2 quadrat sampler (with known efficiency and bias in riffles) from three small streams in the Missouri Ozarks. Triplicate samples (one of each technique) were taken from two creeks and one headwater stream (n=69 sites) over a two-year period. General linear mixed models showed the number of crayfish collected using the quadrat sampler was greater than the number collected using either of the two seine techniques. However, there was no significant interaction with gear suggesting year, stream size, and channel unit type did not relate to different catches of crayfish by gear type. Variation in catch among gears was similar, as was the proportion of young-of-year individuals across samples taken with different gears or techniques. Negative binomial linear regression provided the appropriate relation between the gears which allows correction factors to be applied, if necessary, to relate catches by the kick seine to those of the quadrat sampler. The kick seine appears to be a reasonable substitute to the quadrat sampler in these shallow streams, with the advantage of ease of use and shorter time required per sample.

Comparison of Winter Precipitation Measurements by Six Tretyakov Gauges at the Valdai Experimental Site

Analyses of long-term (1991–2010) intercomparison data quantify the consistency of winter precipitation observations by six identical Tretyakov gauges at the Valdai research station in Russia. Relative to the standard Tretyakov gauge, the mean catch ratios are 97 to 106% for dry snow, 94 to 104% for wet snow, 87 to 109% for blowing snow, 96 to 103% for mixed precipitation, and 98 to 101% for winter rain. The differences between the highest and lowest mean catches are about 10 to 11% for snow, 7% for mixed precipitation, and 3% for rain. On average, this difference is about 0.2 mm over the 12-hour observation period. The catch difference for blowing snow is much higher, up to 22%, or an average of 0.6 mm per observation. Comparisons of 12-hour observations show better consistency in gauge performance for low snowfall events and a large variation in gauge catch for high snowfall events. The differences in 12-hour snow catches are mostly less than 2 mm among the six gauges. The differences in the 12-hour observations are less than 1% for rain and 4% for mixed precipitation. Close linear relationships exist between the 12-hour gauge observations for all precipitation types. The maximum differences in gauge snow catches increase very weakly with wind speed, and higher differences are associated with warmer temperatures, from −5°C to 0°C. There is, however, no significant relationship between the maximum catch difference and the mean wind speed or temperature over the 12-hour period.

A Tale of Two Fishes: Using Recreational Angler Records to Examine the Link Between Fish Catches and Floodplain Connections in a Subtropical Coastal River

In the tropical and subtropical wet and dry regions, maintaining natural hydrologic connections between coastal rivers and adjacent ephemeral wetlands is critical to conserving and sustaining high levels of fisheries production within these systems. Though there is a consensus that there is a need to maintain these natural connections, little is known about what attributes of floodplain inundation regimes are most important in sustaining fisheries production. Two attributes of the flood season and thus floodplain inundation that may be particularly influential to fisheries are the amplitude of the flood season (floodplain water depth and spatial extent of inundation) and the duration of the flood season (i.e., time floodplains are inundated). In mangrove-dominated Everglades coastal rivers, seasonal inundation of upstream marsh floodplains may play an important role in provisioning recreational fisheries; however, this relationship remains unknown. Using two Everglades coastal river fisheries as a model, we tested whether the amplitude of the flood season or the duration of the flood season is more important in explaining variation in angler catch records of common snook and largemouth bass collected from 1992 to 2012. We validated angler catches with fisheries-independent electrofishing conducted in the same region from 2004 to 2012. Our results showed (1) that bass angler catches tracked electrofishing catches, while snook catches were completely mismatched. And (2) that previous year's marsh dynamics, particularly the duration of the flood season, was more influential than the flood season amplitude in explaining variation in bass catches, such that bass angler catches were negatively correlated to the period time that floodplains remained disconnected from coastal rivers in the previous year, while snook catches were not very well explained by floodplain inundation terms.

The summer assemblage of large pelagic Crustacea in the Gully submarine canyon: Major patterns

We describe the trawl-vulnerable crustacean micronekton and macrozooplankton of the Gully, a large, shelf-incising submarine canyon off Nova Scotia, Canada, and a Marine Protected Area. Over 68 species of pelagic crustacea were collected with an International Young Gadoid Pelagic Trawl during three annual summer surveys at one fixed station in the canyon. Depths sampled ranged from the surface to the upper bathypelagic zone, concentrated in the upper 1250m, with a maximum depth of 1500m. The crustacean fauna was dominated by cold temperate species typical of mid- to higher-latitudes in the North Atlantic. Meganyctiphanes norvegica and Eusergestes arcticus were particularly dominant in terms of both observed biomass and abundance above 750m depth. At least 17 species were new records for Canadian waters. The species assemblage of the station varied primarily with depth and diel cycle, the only dominant members of the assemblage showing pronounced inter-annual variations in catch being M. norvegica and Themisto gaudichaudii, both relatively shallow living species.

Rising catch variability preceded historical fisheries collapses in Alaska

Statistical indicators such as rising variance and rising skewness in key system parameters may provide early warning of "regime shifts" in communities and populations. However, the utility of these indicators has rarely been tested in the large, complex ecosystems that are of most interest to managers. Crustacean fisheries in the Gulf of Alaska and Bering Sea experienced a series of collapses beginning in the 1970s, and we used spatially resolved catch data from these fisheries to test the predictions that increasing variability and skewness would precede stock collapse. Our data set consisted of catch data from 14 fisheries (12 collapsing and two non-collapsing), spanning 278 cumulative years. Our sampling unit for analysis was the Alaska Department of Fish and Game statistical reporting area (mean n for individual fisheries = 42 areas, range 7-81). We found that spatial variability in catches increased prior to stock collapse: a random-effects model estimating trend in variability across all 12 collapsing fisheries showed strong evidence of increasing variability prior to collapse. Individual trends in variability were statistically significant for only four of the 12 collapsing fisheries, suggesting that rising variability might be most effective as an indicator when information from multiple populations is available. Analyzing data across multiple fisheries allowed us to detect increasing variability 1-4 years prior to collapse, and trends in variability were significantly different for collapsing and non-collapsing fisheries. In spite of theoretical expectations, we found no evidence of pre-collapse increases in catch skewness. Further, while models generally predict that rising variability should be a transient phenomenon around collapse points, increased variability was a persistent feature of collapsed fisheries in our study. We conclude that this result is more consistent with fishing effects as the cause of increased catch variability, rather than the critical slowing down that is the driver of increased variability in regime shift models. While our results support the use of rising spatial variability as a leading indicator of regime shifts, the failure of our data to support other model-derived predictions underscores the need for empirical validation before these indicators can be used with confidence by ecosystem managers.

Analysis on responses of hairtail catches to fishing and climate factors in the Yellow Sea and Bohai Sea, China

Changes in fish harvest are not only impacted by fishing,but also influenced by climate variability.Based on data of hairtail catches between 1956 and 2006 in the Yellow Sea and Bohai Sea,China,the responses of catches to fishing and climate factors were analyzed.The catch time series can be compartmentalized into an in-ter-annual trend and variations.The inter-annual trend was mainly attributed to growth in fishing efforts.This was suggested by highly significant regression of hairtail catches to fishing effort fitted by the Fox model(P0.01).After the catch trend was removed,there were positive partial correlations(P0.02) of the residual variations in catches to winter wind speed in the Yellow Sea,summer wind speed in the East China Sea,and annual precipita-tion in Yellow River Valley and the coastal region of the Yellow Sea and Bohai Sea,whereas the partial correla-tions to sea surface temperature and summer wind speed in the Yellow Sea,as well as summer and winter wind speeds in the Bohai Sea were negative(P0.05).The linkage suggests that the climate factors govern the hairtail catch variations.It was inferred that runoff input nutrients to the Yellow Sea and Bohai Sea,while monsoons con-trolled the transport and distribution of the nutrients,and these processes can have impacts on the primary produc-tivity.Changes in water temperature could also directly affect the growth,feeding,spawning,and migration of the fish,and thus,influence the fish population size.The hairtail catch time series can be jointly fitted by fishing ef-fort and climatic factors(P0.01),suggesting that,in addition to fishing,climate factors can significantly influ-ence the hairtail catches.In the context of global warming,it was projected that the future climate changes would lead to reduction in hairtail production in the Yellow Sea and Bohai Sea,and the hairtail catch variations would become even greater.

Evaluating alternative management strategies for bigeye tuna, &lt;i&gt;Thunnus obesus&lt;/i&gt;, in the Indian Ocean

Bigeye tuna ( Thunnus obesus ) support a large commercial fishery in the Indian Ocean. However, explicit management strategies and harvest control rules are yet to be developed for the management of this fishery. We used a stochastic age-structured production model as an operating model to evaluate several potential management strategies under different assumptions of stock productivity. Five management strategies—constant fishing mortality, constant catch, quasi-constant catch, constant escapement, and status-dependent strategies—were evaluated and compared using the performance indicators including average catch, average spawning stock biomass, variation in catch, average fishing mortality and lowest biomass during the time period considered in the simulation. This study shows that (1) for the constant catch strategy, an annual catch of 90000 t would result in a low risk of stock being overfished while obtaining a stable catch; (2) for the constant fishing mortality strategy fishing mortality of 0.3 per year could yield a higher catch, but might have a high probability (64%) of stock dropping below the spawning stock biomass (SSB) that could achieve maximum sustainable yield ( SSB msy ); and (3) for the quasi-constant catch strategy an annual catch of 110000 t was sustainable if the current SSB was higher than SSB msy . Constant escapement and status-dependent strategies were robust with respect to different levels of virgin recruitment and steepness. This study suggests that it is important to incorporate uncertainties associated with key life history, fisheries and management processes in evaluating management strategies.

Influence of soak time and fish accumulation on catches of reef fishes in a multispecies trap survey

Catch rates from fishery-independent surveys often are assumed to vary in proportion to the actual abundance of a population, but this approach assumes that the catchability coefficient (q) is constant. When fish accumulate in a gear, the rate at which the gear catches fish can decline, and, as a result, catch asymptotes and q declines with longer fishing times. We used data from long-term trap surveys (1990–2011) in the southeastern U.S. Atlantic to determine whether traps saturated for 8 reef fish species because of the amount of time traps soaked or the level of fish accumulation (the total number of individuals of all fish species caught in a trap). We used a delta-generalized-additive model to relate the catch of each species to a variety of predictor variables to determine how catch was influenced by soak time and fish accumulation after accounting for variability in catch due to the other predictor variables in the model. We found evidence of trap saturation for all 8 reef fish species examined. Traps became saturated for most species across the range of soak times examined, but trap saturation occurred for 3 fish species because of fish accumulation levels in the trap. Our results indicate that, to infer relative abundance levels from catch data, future studies should standardize catch or catch rates with nonlinear regression models that incorporate soak time, fish accumulation, and any other predictor variable that may ultimately influence catch. Determination of the exact mechanisms that cause trap saturation is a critical need for accurate stock assessment, and our results indicate that these mechanisms may vary considerably among species.

Within‐Day Variability in Catch Taken by Public Access Fishers during a Recreational Fishing Survey

AbstractAccess point surveys of recreational fisheries are usually stratified into weekdays and weekend days and allocate only a single sampling assignment per day sampled; this is because most variation is thought to be due to differences in angler behavior between the week and weekend and between days. However, few estimates of within‐day variability are available, and this source of error has not been adequately assessed. During a 2011 survey of the recreational fishery for blue crabs Callinectes sapidus in Maryland, we used a stratified two‐stage design with week and weekend strata, and multiple assignments were selected randomly within sampling days to measure within‐day variability. Within‐day variability accounted for 85.3–98.5% of the variation in blue crab catch between July and September, whereas 1.5–14.7% of the variation was due to between‐day variability; during the months examined, there was no significant effect due to week–weekend. These results suggest the use of a simple two‐stage design to estimate the recreational catch of blue crabs, with sampling effort allocated to capturing within‐day variability. Better management of the main sources of error can increase the precision and accuracy of catch estimates, and we recommend that recreational surveys use pilot studies to evaluate sources of variation before the study design is finalized.