Inform Fisheries Management Research Articles

Use of underwater video to assess freshwater fish populations in dense submersed aquatic vegetation

Underwater video cameras (UVC) provide a non-lethal technique to sample fish in dense submersed aquatic vegetation. Fish often inhabit densely vegetated areas, but deficiencies of most sampling gears bias relative abundance estimates that inform fisheries management. This study developed methods using UVC to estimate relative abundance in dense vegetation using three experimental ponds covered with surface-matted hydrilla (Hydrilla verticillata) stocked at different densities of Lepomis spp. and largemouth bass (Micropterus salmoides). We conducted UVC point counts over 13 weeks to measure relative fish abundance and occurrence from video analysis. Ponds were then drained to obtain true fish densities. In total, fish were detected in 55% of all counts and juvenile and adult Lepomis spp. and largemouth bass were enumerated. End-of-season true fish densities ranged across ponds (from 52 to 37000 fishha–1). Additionally, pond 2’s true density changed substantially from 370 to 12300 fishha–1. True population size was accurately reflected in differences in estimated relative abundances obtained from fish counts, as in pond 2 where mean fish counts increased from 0.10 in week 1 to 2.33 by week 13. Underwater video accurately and precisely quantified relative abundance at naturally-occurring fish densities, but this success was reduced at low densities.

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.

Mapping inshore fisheries: Comparing observed and perceived distributions of pot fishing activity in Northumberland

Marine spatial planning (MSP) is increasingly promoted as part of an ecosystem-based approach to marine resource management. Impacts of MSP may be particularly great in inshore fisheries, yet despite their vulnerability, assessing potential impacts of spatial measures on inshore fisheries is limited by data scarcity, and the comparability of patterns of fishing activity produced by different data sources is poorly understood. This study contributes to the debate around information needs for MSP by describing the distribution of lobster potting activity at four ports in Northumberland, UK, using two sources of spatial data: observed fishing vessel sightings by patrol vessels and perceived fishing activity elicited through interviews with local fishers. The comparability of the distributions of potting activity mapped by the two datasets was explored using Mantel tests and overlap of fishing hotspots identified. Fishing activity at all ports tended towards an aggregated or patchy distribution, with hotspots located in inshore areas in close proximity to vessels׳ home ports. The two datasets were correlated at each port, though the strength of correlation varied among ports, being greater in ports with more highly aggregated fishing activity. Results suggest that vessel sightings are likely to better represent variable intensity of fishing activity, while interview data may more accurately capture the absolute extent of grounds important to fishers. This study highlights some of the merits and limitations of two available data sources currently used to inform fisheries management and marine conservation planning, and outlines an approach to assessing the consistency of datasets in describing the spatial distribution of activity. Given the limitations of individual datasets, we recommend triangulation of available data to inform MSP, alongside qualitative data on fishers׳ behaviour.

Reproductive biology of Chinese minnow Hemiculterella sauvagei Warpachowski, 1888 in the Chishui River, China

This study describes the reproductive biology of the Chinese minnow Hemiculterella sauvagei. The length-weight relationship, sex ratio, spawning season, size at first maturity, and fecundity were analyzed based on 685 specimens collected from the Chishui River between July 2011 and July 2012. The relationship between standard length (SL) and body weight (BW) were estimated as BW=2.14x10(-4)xSL(2.801) (R-2=0.839; N=413; P 12cm. Analyses of the monthly variation in the gonadosomatic index (GSI), the monthly proportions of macroscopic gonadal maturity, and the size distribution of oocytes consistently suggested a prolonged spawning season of H.sauvagei from March to August, with a peak from April to May. Logistic curves describing the relationship between proportion of maturity (P-r) at each length interval and standard length were estimated as P-r=1/(1+e(26.867-0.306SL)) (R-2=0.999; N=413; P<0.05) for females and P-r=1/(1+e(10.522-0.142SL)) (R-2=0.999; N=272; P<0.05) for males. Size at first maturity was estimated as 7.4cm for males and 8.8cm SL for females. Absolute fecundity varied from 563 to 5052, with a mean of 2413 +/- 874 oocytes per ovary. The relative fecundity was estimated to be 41-299, with a mean of 171 +/- 55 oocytes per ovary. The present study provides useful information for fishery management and resources conservation.

More analytical bite in estimating targets for shark harvest

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 488:221-232 (2013) - DOI: https://doi.org/10.3354/meps10375 More analytical bite in estimating targets for shark harvest Corey J. A. Bradshaw1,2,*, Iain C. Field3, Clive R. McMahon4, Grant J. Johnson5, Mark G. Meekan6, Rik C. Buckworth5,7 1The Environment Institute and School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia 2South Australian Research and Development Institute, PO Box 120, Henley Beach, South Australia 5022, Australia 3Graduate School of the Environment, Macquarie University, Sydney, New South Wales 2109, Australia 4Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Northern Territory 0909, Australia 5Northern Territory Fisheries, Department of Primary Industry and Fisheries, GPO Box 3000, Darwin, Northern Territory 0801, Australia 6Australian Institute of Marine Science, UWA Oceans Institute (M096), 35 Stirling Hwy, Crawley, Western Australia 6009, Australia 7CSIRO Marine and Atmospheric Research, Wealth from Oceans Flagship, GPO Box 2583, Brisbane, Queensland 4001, Australia *Email: corey.bradshaw@adelaide.edu.au ABSTRACT: The typically slow life histories of sharks make them susceptible to overexploitation. However, this characteristic also means that shark populations are more amenable to mark-recapture estimation of vital rates and to population viability analysis, compared to many teleost (bony) fishes. We applied this novel approach to inform fisheries management for 2 shark species (Carcharhinus tilstoni and C. sorrah) in northern Australia. We calculated survival estimates based on a current mark-recapture study and age-frequency distributions from historical catch data, and used these along with other estimates of vital rates to construct an individual-based population viability analysis (using VORTEX software). We estimated total current mortality (natural and fishing-related) from tagging data using Brownie models (mean ± SE: 0.532 ± 0.097 and 0.487 ± 0.136) and recapture rate (fisheries-related mortality) (0.023 ± 0.005 and 0.008 ± 0.003) for C. tilstoni and C. sorrah, respectively. Based on historical age-at-length and age-frequency data, mean survival across ages after historical overexploitation was similar for both species (~0.43, or ~0.33 as an age frequency-weighted mean). After correcting for capture-related mortality and permanent emigration, VORTEX population projections including incrementing simulated harvest suggest that the current rates of harvest of both species result in population trajectories that are approximately stable (20 yr predicted average rate of population change r ≅ 0), but this is complicated by a variable contribution of the slower-reproducing species C. limbatus within the black-tip shark complex (C. limbatus is commonly misidentified as C. tilstoni in the fishery). VORTEX projections also clearly indicated that the fishery was overexploited in the past. Using multiple datasets and an individual-based modelling framework to estimate harvest limits for a commercial fishery provides novel insights into management. This is especially pertinent to shark populations given the relative tractability of marking and recovering individuals and the inherent susceptibility of shark populations to overexploitation. KEY WORDS: Harvest · Fisheries · Survival · Life table · Demography · VORTEX · Carcharhinus tilstoni · Carcharhinus sorrah · Carcharhinus limbatus Full text in pdf format PreviousNextCite this article as: Bradshaw CJA, Field IC, McMahon CR, Johnson GJ, Meekan MG, Buckworth RC (2013) More analytical bite in estimating targets for shark harvest. Mar Ecol Prog Ser 488:221-232. https://doi.org/10.3354/meps10375 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 488. Online publication date: August 15, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Using fisheries by‐catch data to predict octocoral habitat suitability around South Georgia

AbstractAimFor many deep‐sea fisheries, there is an urgent management requirement for information on the presence of vulnerable marine ecosystems (VMEs). Gathering deep‐sea data using conventional techniques can be expensive and time‐consuming. One way to provide a relatively rapid assessment of VME presence is to use data from fisheries by‐catch and historical scientific observations. Our aim was to predict suitable habitat for octocorals around South Georgia and to estimate the extent to which octocoral habitat is currently protected by fisheries management measures. In addition, we attempted to determine the types of terrain in which octocorals and fishing activities occur.LocationSouth Georgia, sub‐Antarctic.MethodsA terrain map of South Georgia was created using Benthic Terrain Modeler (BTM). Georeferenced octocoral data were combined with environmental layers to create an octocoral habitat suitability map using ecological niche factor analysis (ENFA).ResultsMost octocoral by‐catch samples originated from narrow crest (an area representing shelf break and moraines) and steep (continental) slope terrains. Calcite saturation state and apparent oxygen utilization (AOU) were the most influential environmental parameters in determining highly suitable octocoral habitat. The ENFA model highlighted shelf‐break areas to be highly suitable habitat for octocorals and that 38% of this habitat around South Georgia lies within areas currently protected by fisheries management; a further 20% is below the 2000‐m fishing depth, meaning effectively that 58% of predicted highly suitable octocoral habitat is currently protected. Although these results indicate protection levels for octocoral habitat well above international standards/targets, the fishery remains active within a relatively concentrated shelf area at 700–2000 m, potentially having a large impact on the 42% of highly suitable octocoral habitat predicted to lie at these depths.Main conclusionsThis research demonstrates the potential for using fisheries by‐catch data to create habitat suitability maps that can inform fisheries management and future research.

Exploiting genetic diversity to balance conservation and harvest of migratory salmon

Population-based management is central to the conservation of highly exploited species. Managing to sustain population diversity is especially challenging for migratory species. The aggregate of populations of sockeye salmon (Oncorhynchus nerka) that spawn in drainages of Bristol Bay, Alaska, is the most abundant in the world and supports the largest high-value salmon fishery in North America. We applied molecular tools (genetic data from 38 single nucleotide polymorphisms, assayed in 96 populations) to detect migratory trends in stock composition of sockeye salmon returning to Bristol Bay and to inform fisheries management in real time. We reliably and repeatedly detected abundances that were unanticipated based upon preseason forecasts, fishing effort was shifted accordingly, and the fleet and local economies benefited while the risk of overharvesting weaker stocks was minimized. This approach is being developed for other species and fisheries and provides a useful model for conservation wherever migrating species are intensely managed.

Geographical variation in size at the onset of maturity of male and female Norway lobster Nephrops norvegicus (L., Homarida: Decapoda) in Scottish waters

Geographical variation in the size at the onset of maturity (‘SOM’) of male and female Norway lobster (Nephrops norvegicus) in Scottish stocks was assessed using estimates based on eleven morphometric measurements analysed using segmented regression analysis. Significant differences were found in SOM in males, with lower values found in areas characterized by high population densities. Specifically, estimates of male SOM for the stocks in the Firth of Forth, Clyde and Sound of Jura were lower, than those estimated for the stocks of the North Minch, which in turn were lower than those of Noup, Moray Firth and Fladen. Differences were consistent across a range of morphometric measurement pairs. In high density areas, males mature at the same carapace length as females and at smaller body sizes than males in low density areas. Estimates of SOM in females, based on morphometric analyses, did not vary significantly across the analysed stocks, and were higher than those derived using traditional maturity assessment methods (maturity ogives). The potential for behavioural, density dependant and environmental modulation of SOM in the Norway lobster is discussed. Improved understanding of the maturation process and associated growth stanza would improve estimation of SOM in Nephrops and inform fisheries management measures aimed at protecting stock reproductive potential.

Capabilities of the Lamont-Doherty Earth Observatory in situ cosmogenic 14C extraction laboratory updated

The three eastern boundary ecosystems comparable to the Benguela ecosystem (BCE) display differences and commonalities. The California (CalCE) and Humboldt Current (HCE) ecosystems are continuous topographically, whereas the Canary Current ecosystem (CanCE) is interrupted by the Gulf of Cadiz and the Canaries archipelago. All have similar regimes of equatorward flow over shelf and slope associated with upwelling and a subsurface poleward flow over the slope, though in the HCE multiple flows and counter-flows appear offshore. All systems exhibit year round upwelling in their centre and seasonal upwelling at their extremes as the trade wind systems that drive them migrate north and south, though the HCE is strongly skewed toward the equator. All systems vary on scales from the event or synoptic scale of a few days, through seasonal, to inter-decadal and long term. Productivity of each system follows the upwelling cycle, though intra-regional variations in nutrient content and forcing cause significant variability within regions. The CanCE is relatively unproductive compared to the CalCE and HCE as a result of differences in large scale circulation between the Pacific and Atlantic. The latter two systems are dominated by El Niño-Southern Oscillation (ENSO) variability on a scale of 4–7 years. Physical modeling with the Princeton Ocean Model and the Regional Oceanic Modeling System has advanced recently to the stage of reproducing realistic mesoscale features and energy levels with climatic wind forcing. Operational forecasting by these models with assimilation of sea surface temperature and other data is successfully implemented in CalCE. On longer time scales, the Lamont-Doherty Earth Observatory model is able to hindcast El Niño variability over the long term up to 2 years in advance. Empirical ecological models in all three systems have attempted prediction of permissible catch level (fractional Maximum Sustainable Yield), recruitment, catches or onset of migration with lack of continued success, partly because discontinuous or inadequate observations hamper model implementation and assessment. Moreover, empirical models tuned to particular environments fail when fundamental regime shifts occur. One of the most successful approaches is that of intensive monitoring of catch and environmental parameters linked to an informal Operational Management Procedure (OMP) to inform fisheries management off Peru. This OMP contributed to preservation of anchovy stock during the 1997-8 El Niño but remains to be formalized or tested under varying conditions. Prediction on time scales of global warming are uncertain because physical climate models still disagree on whether upwelling will intensify or weaken. Possible scenarios on decadal scale based on warming or cooling of waters in the Eastern Boundary Current systems can be proffered, albeit with little confidence at present. Future approaches for all systems, including the BCE, will in the long run likely combine coupled atmospheric/ocean models with biological process models. Judicious application of purely statistical modeling based on inherent time series properties will assist, though such techniques are unable to cope with regime shifts.

Population genetics of tunas in South China Sea inferred from control regions

The South China Sea(SCS)surrounded by the first island chain is a semi-enclosed sea linking the Indian Ocean and the Pacific Ocean.The population genetic features of the two most important economic species,yellowfin tuna(YFT,Thunnus albacares,17 adults and 44 juveniles)and big eye tuna(BET,T.obesus,22 adults and 4 juveniles)in SCS(11-12°N,15°N;110-112°E),have been analyzed based on the partial mitochondrial D-loop sequences.Our data supported the following conclusions:(1) both species were high nucleotide variation with very high haplotype diversities(Hd99%),while the evidence from fixation indexes,and cluster trees showed the population diversity of BET was higher than those of YFT;(2) For BET and YFT,the strongest gene flow between populations in SCS and the Indian Ocean were 51.638 and 261.280 10,then the Pacific by 10.868 8 and-50.801 81,respectively;(3) both species obey the sudden expansion model.Contrasted with the unimodal of YFT,the mismatch distribution of BET,as well as the SCS population,were bimodal.Moreover,the spanning time of SCS population of BET was later inferred from the Tau(=7.902)with biggest spanning scale(θ1/θ0=99 999/14.752).The results should be basic information for fisheries management,fishing quotas determination as well for aquaculture of tuna.

Detection of outlier loci and their utility for fisheries management.

Genetics-based approaches have informed fisheries management for decades, yet remain challenging to implement within systems involving recently diverged stocks or where gene flow persists. In such cases, genetic markers exhibiting locus-specific (‘outlier’) effects associated with divergent selection may provide promising alternatives to loci that reflect genome-wide (‘neutral’) effects for guiding fisheries management. Okanagan Lake kokanee (Oncorhynchus nerka), a fishery of conservation concern, exhibits two sympatric ecotypes adapted to different reproductive environments; however, previous research demonstrated the limited utility of neutral microsatellites for assigning individuals. Here, we investigated the efficacy of an outlier-based approach to fisheries management by screening >11 000 expressed sequence tags for linked microsatellites and conducting genomic scans for kokanee sampled across seven spawning sites. We identified eight outliers among 52 polymorphic loci that detected ecotype-level divergence, whereas there was no evidence of divergence at neutral loci. Outlier loci exhibited the highest self-assignment accuracy to ecotype (92.1%), substantially outperforming 44 neutral loci (71.8%). Results were robust among-sampling years, with assignment and mixed composition estimates for individuals sampled in 2010 mirroring baseline results. Overall, outlier loci constitute promising alternatives for informing fisheries management involving recently diverged stocks, with potential applications for designating management units across a broad range of taxa.

Red Snapper in the Gulf of Mexico and U.S. South Atlantic: Data, Doubt, and Debate

AbstractStock assessments provide fisheries managers with information that is used in the regulation of a fish stock. Assessments often rely upon a wide array of biological and fisheries data of varying quantity and quality, making the assessment process data hungry, complex, and uncertain. Assessment scientists face the difficulty of estimating numbers of individuals (among other biological benchmarks) of a population of widely distributed, often mobile, fishes for which direct measurement of almost everything is impossible. Consequently, stock assessment scientists are forced to use tools designed to assemble a variety of indirect measures into a statistical model capable of producing predictions to inform fisheries management about stock status and the consequences of past, current and future fishing practices. Despite large differences in estimates of the status of red snapper stocks in the Gulf of Mexico (U.S.) and south Atlantic Ocean (U.S.), and the management conclusions and decision drawn from these assessments, there are more similarities than differences in the basic data being used to inform assessment models, as well as in model outcomes concerning trends in biomass, catch‐at‐age and stock productivity. There are key differences in some of these data, and in how historical landings and uncertainty is handled in the assessment process, that result in large differences between the two management regions in beliefs about current and future productivity of red snapper stocks, and regulatory measures necessary for reaching management goals.

Artificial reef placement: a red snapper, Lutjanus campechanus, ecosystem and fuzzy rule-based model

Abstract This study on reef placement involves two aspects: (1) the development of a bioenergetics model for red snapper, Lutjanus campechanus (Poey), in Gulf of Mexico waters off the coast of Alabama, where significant numbers of artificial reefs are thought to exist, and (2) a fuzzy rough set model by which parameters determined from the bioenergetics model can provide a decision tool for optimally spacing artificial reefs during deployment. The bioenergetics and consumption rates of L. campechanus by age class foraging on artificial reefs in the Gulf of Mexico off the coast of Alabama provided input into the fuzzy rule-based model. After conducting multiple simulations, highest certainty in optimal reef spacing was achieved for reef distances between 0.50 and 0.95 km such that no more than two fit within a 1-km2 area. Results can inform fisheries managers about placement of artificial reefs to affect the health and survival of reef-associated species.

Estimating Demand for Urban Fisheries Management: an Illustration of Conjoint Analysis as a Tool for Fisheries Managers

AbstractThis paper illustrates the use of discrete‐choice analysis, a nonmarket valuation technique, for assessing the effect of different management or fishing site quality variables on demand for urban fisheries. The study was carried out in three fishing ponds that are a part of the Close‐to‐Home Fishing Program in the Oklahoma City metropolitan area. We found that, on average, anglers were willing to pay more for physical infrastructure improvements, such as flush toilets ($3.81/year) and docks ($1.28/year), than for having larger channel catfish Ictalurus punctatus stocked (.23/year for a 4‐in increase). Willingness to pay for improvements to the ponds was less for minority anglers than for other anglers. Having relative values for potential management changes for a fishery helps to inform fisheries managers about what characteristics are valued most by anglers, allowing managers to better serve the anglers' interest and to justify the costs of implementing these changes.

Multi-stakeholder perspectives on the use and influence of “grey” scientific information in fisheries management

Abstract Scientific information on the shrimp and groundfish resources of the Brazil–Guianas continental shelf has been produced by the United Nations Food and Agriculture Organization (FAO) and the Caribbean Regional Fisheries Mechanism (CRFM), in collaboration with the national governments exploiting the resources, since the early 1970s. In spite of the availability of such information, largely as grey literature, there is limited evidence as to the extent it is being used in fisheries management in Trinidad and Tobago. The flow of information between multiple stakeholders − fishing industry, scientists, fisheries managers, policy makers, and fisheries advisory bodies − was studied based on responses to a survey of key individuals to document each of their roles in the creation, distribution, and use of fisheries information. Content analysis of responses was completed to determine the opportunities and barriers for using scientific information in fisheries management. Salience, credibility, and legitimacy of the information were shadowed by barriers that decreased these attributes. Knowledge about the fishery has increased and technical capabilities have been strengthened through research. At the same time, advances in digital technology have made information more accessible. Yet, the high technical content of fisheries information reduced its usefulness to some stakeholders and formal systems do not exist for distributing or measuring the use and influence of such information in decision making. Communication strategies to promote awareness of the scientific information and aligning scientific information with fisheries policy could increase its use and influence. Institutional support for partnerships and education to encourage stakeholder involvement could also facilitate increased influence of scientific information.

Modeling the Influence of Environmental Factors on Spawning Migration Mortality for Sockeye Salmon Fisheries Management in the Fraser River, British Columbia

AbstractThe impact of freshwater environmental factors on spawning migration mortality was modeled to provide a predictive tool for fisheries management of four run timing groups of Fraser River sockeye salmon Oncorhynchus nerka: early Stuart (Stuart Lake), early summer, summer, and late. We tested the significance of different measures of water temperature, discharge, fish abundance, and entry timing for forecasting discrepancies between lower‐river and upriver escapement estimates using multiple regressions of principal component scores. Descriptive discrepancy models (i.e., “management adjustment” models) identified using Akaike's information criterion were consistent with the known biology of each group. For example, temperature and discharge thresholds were selected for early Stuart run discrepancy models, reflecting the extremes in both variables experienced by these early migrants. Predictive discrepancy models were also generated for each run timing group by using the limited number of environmental variables that are available in‐season to fisheries managers. Even predictive discrepancy models using simple environmental metrics of average river temperature, flow, and river entry timing provide a valuable tool for forecasting relative indices of spawning migration mortality. This study provides an example of how environmentally based predictive tools can be used to inform fisheries management decisions and improve the probability of achieving spawning escapement targets.

The value of information in fisheries management: North Sea herring as an example

Abstract Mäntyniemi, S., Kuikka, S., Rahikainen, M., Kell, L. T., and Kaitala, V. 2009. The value of information in fisheries management: North Sea herring as an example. – ICES Journal of Marine Science, 66: 2278–2283. We take a decision theoretical approach to fisheries management, using a Bayesian approach to integrate the uncertainty about stock dynamics and current stock status, and express management objectives in the form of a utility function. The value of new information, potentially resulting in new control measures, is high if the information is expected to help in differentiating between the expected consequences of alternative management actions. Conversely, the value of new information is low if there is already great certainty about the state and dynamics of the stock and/or if there is only a small difference between the utility attached to different potential outcomes of the alternative management action. The approach can, therefore, help when deciding on the allocation of resources between obtaining new information and improving management actions. In our example, we evaluate the value of obtaining hypothetically perfect knowledge of the type of stock–recruitment function of the North Sea herring (Clupea harengus) population.

Size matters: variation in the diet of chick and adult crested terns

We investigated ontogenetic, temporal and spatial patterns in the composition and size of prey in the diet of crested terns, Sterna bergii. Diet analyses indicated that crested terns are a generalist predator on surface-schooling clupeids (Australian anchovy Engraulis australis, sardine Sardinops sagax and blue sprat Spratelloides robustus), Degens leatherjacket Thamnaconus degeni, southern sea garfish Hyporhamphus melanochir, Australian herring Arripis georgianus, slender bullseye Parapriacanthus elongatus and barracouta Thyrsites atun. Ontogenetic differences in prey size indicated that adults are constrained in their foraging behaviour during the early chick-provisioning period by the need to self feed and select smaller prey that can be ingested by their chicks. Chicks consumed significantly higher proportions of clupeids than adults, which consumed mainly Degens leatherjackets and barracouta, suggesting that adults may select higher quality prey for their chicks compared to what they consume themselves. Spatial differences in prey composition were driven by differing proportions of sardine, Australian anchovy and Degens leatherjacket and could reflect local differences in the abundances of these prey. The size of prey taxa consumed by adults also reflected a North–South gradient in prey size. The large component of juvenile sardine in the diet of crested terns suggests future dietary measures may inform fisheries managers about changes in local juvenile sardine abundance. These data could assist in highlighting any fishery-related decreases in sardine recruitment and help ensure commercial fishing practices address principals of Ecologically Sustainable Development developed for Australian fisheries.

Energy Content of Young Alewives in Eastern Lake Michigan and Muskegon Lake, a Connected Drowned River Mouth Lake

AbstractEnergy content is an important determinant of an individual fish's condition and a key input variable for bioenergetics applications. Energy content of young fish can change rapidly during ontogeny; given the numerical abundance and high mass‐specific metabolic rates of young fish, it is particularly important to obtain detailed information on their energy content. To this end, we quantified the total body energy content and energy density of economically and ecologically important young (age‐0–1) nonnative alewives Alosa pseudoharengus collected during 1998–2003 in eastern Lake Michigan and Muskegon Lake, a connected drowned river mouth lake. Our analysis demonstrates that energy content of young alewives varies across years, seasons, lakes, and ontogeny. Consistent with previous observations of size‐dependent overwinter mortality, young alewives deplete a large amount of body energy between late fall and late spring (i.e., declines in length‐specific energy content and energy density occur overwinter). Interestingly, unlike several past studies of young fish in their native range, size‐specific energy content of young alewives does not appear to increase over the summer and fall (there is no evidence of increased energy storage in preparation for the resource‐scarce winter period). Finally, our measured values are similar to the few previously published energy density values for age‐0 alewives. The high degree of variation in the energy content of young fish emphasizes the necessity of using appropriate energy measures for bioenergetics applications to inform fisheries management.

Figuring Out the Human Dimensions of Fisheries: Illuminating Models

AbstractBoth natural scientists and economists commonly use quantitative data to create models of the systems that interest them and then use these models to inform fisheries management. Other social scientists rely on lengthier, descriptive texts based primarily on qualitative data to assess the human dimensions. To their dismay, fisheries social scientists find that much of their rich narrative with keen insights ends up filling pages that are neither read nor meaningfully integrated into decision‐making in fisheries management. Nevertheless, what all scientists, practitioners, and managers want and need is information that will lead to a better understanding of the ecosystem (comprised of interdependent ecological and human systems) and therefore to fisheries management that benefits the whole system. Based on the belief that only a combination of high‐quality quantitative and qualitative data will provide both the numbers and the context needed for success in ecosystem‐based management, we discuss efforts to present social and cultural information in forms that are more familiar to those who rely on models for a representation of reality in the fisheries context. We point out how the designers of these models (or how we) think the models might be applied to fisheries management, noting how each model attempts to incorporate qualitative data to depict context essential for grounding the more commonly used biological and economic models. We also assess the benefits and limitations of these models, including the constraints on their development and use.