Jeremy S. Collie

Rebuilding Global Fisheries

Fighting for Fisheries In the debate concerning the future of the worlds fisheries, some have forecasted complete collapse but others have challenged this view. The protagonists in this debate have now joined forces to present a thorough quantitative review of current trends in world fisheries. Worm et al. (p. 578) evaluate the evidence for a global rebuilding of marine capture fisheries and their supporting ecosystems. Contrasting regions that have been managed for rebuilding with those that have not, reveals trajectories of decline and recovery from individual stocks to species, communities, and large marine ecosystems. The management solutions that have been most successful for rebuilding fisheries and ecosystems, include both large- and small-scale fisheries around the world. Catch restrictions, gear modification, and closed areas are helping to rebuild overexploited marine ecosystems. After a long history of overexploitation, increasing efforts to restore marine ecosystems and rebuild fisheries are under way. Here, we analyze current trends from a fisheries and conservation perspective. In 5 of 10 well-studied ecosystems, the average exploitation rate has recently declined and is now at or below the rate predicted to achieve maximum sustainable yield for seven systems. Yet 63% of assessed fish stocks worldwide still require rebuilding, and even lower exploitation rates are needed to reverse the collapse of vulnerable species. Combined fisheries and conservation objectives can be achieved by merging diverse management actions, including catch restrictions, gear modification, and closed areas, depending on local context. Impacts of international fleets and the lack of alternatives to fishing complicate prospects for rebuilding fisheries in many poorer regions, highlighting the need for a global perspective on rebuilding marine resources.

A quantitative analysis of fishing impacts on shelf-sea benthos

1. The effects of towed bottom-fishing gear on benthic communities is the subject of heated debate, but the generality of trawl effects with respect to gear and habitat types is poorly understood. To address this deficiency we undertook a meta-analysis of 39 published fishing impact studies. 2. Our analysis shows that inter-tidal dredging and scallop dredging have the greatest initial effects on benthic biota, while trawling has less effect. Fauna in stable gravel, mud and biogenic habitats are more adversely affected than those in less consolidated coarse sediments. 3. Recovery rate appears most rapid in these less physically stable habitats, which are generally inhabited by more opportunistic species. However, defined areas that are fished in excess of three times per year (as occurs in parts of the North Sea and Georges Bank) are likely to be maintained in a permanently altered state. 4. We conclude that intuition about how fishing ought to affect benthic communities is generally supported, but that there are substantial gaps in the available data, which urgently need to be filled. In particular, data on impacts and recovery of epifaunal structure-forming benthic communities are badly needed.

Long-term shifts in the species composition of a coastal fish community

To study decadal shifts in a coastal nekton community, we analyzed data on 25 fish and invertebrate species collected from 1959 to 2005 by the University of Rhode Island, Graduate School of Oceanography (Narragansett, Rhode Island, USA). This weekly trawl survey samples two locations: inside Narragansett Bay and in Rhode Island Sound. Over four decades, the community has shifted progressively from vertebrates to invertebrates and, especially since 1980, from benthic to pelagic species. Demersal species that declined include winter flounder (Pseudopleuronectes americanus), silver hake (Merluccius bilinearis), and red hake (Urophycis chuss); meanwhile warm-water fish (butterfish, Peprilus triacanthus; scup, Stenotomus chrysops) and invertebrates (lobster, crab, squid) increased with time. Total numbers reached a maximum in the 1990s, while mean body size decreased. Taxonomic diversity increased over time, as the community shifted from fish to invertebrates of several phyla. The shifts in species composition...

Sustainability in single–species population models

In this paper, we review the concept of sustainability with regard to a single–species, age–structured fish population with density dependence at some stage of its life history. We trace the development of the view of sustainability through four periods. The classical view of sustainability, prevalent in the 1970s and earlier, developed from deterministic production models, in which equilibrium abundance or biomass is derived as a function of fishing mortality. When there is no fishing mortality, the population equilibrates about its carrying capacity. We show that carrying capacity is the result of reproductive and mortality processes and is not a fixed constant unless these processes are constant. There is usually a fishing mortality, FMSY, which results in MSY, and a higher value, Fext, for which the population is eventually driven to extinction. For each F between 0 and Fext, there is a corresponding sustainable population. From this viewpoint, the primary tool for achieving sustainability is the control of fishing mortality. The neoclassical view of sustainability, developed in the 1980s, involved population models with depensation and stochasticity. This view point is in accord with the perception that a population at a low level is susceptible to collapse or to a lack of rebuilding regardless of fishing. Sustainability occurs in a more restricted range from that in the classical view and includes an abundance th reshold. A variety of studies has suggested that fishing mortality should not let a population drop below a threshold at 10–20% of carrying capacity. The modern view of sustainability in the 1990s moves further in the direction of precaution. The fishing mortality limit is the former target of FMSY (or some proxy), and the target fishing mortality is set lower. This viewpoint further reduces the range of permissible fishing mortalities and resultant desired population sizes. The objective has shifted from optimizing long–term catch to preserving spawning biomass and egg production for the future. The use of discount rates in objective functions involving catch is not a suitable alternative to protecting reproductive value. As we move into the post–modern time period, new definitions of sustainability will attempt to incorporate he economic and social aspects of fisheries and/or ecosystem and habitat requirements. These definitions now involve ‘warm and fuzzy’ notions (healthy ecosystems and fishing communities, the needs of future generations, diverse fish communities) and value judgements of desired outcomes. Additional work is needed to make these definitions operational and to specify quantitative objectives to be achieved. In addition, multiple objectives may be incompatible, so trade–offs in what constitutes sustainability must be made. The advances made under the single–species approach should not be abandoned in the post–modern era, but rather enhanced and combined with new approaches in the multi–species and economic realms.

Does selective fishing conserve community biodiversity? Predictions from a length-based multispecies model

This study challenges the widely held view that improved fisheries selectivity would always help to maintain marine biodiversity. Using a length-based multi-species model, we investigate the effects of selective versus nonselective fishing on fish communities. Both size and species selectivity are examined, and fishing effects on biodiversity are measured with three indices: (i) evenness, (ii) the number of collapsed species, and (iii) an index of size diversity. The model is parameterized for the Georges Bank and North Sea fish communities. The results suggest that there is no “optimal” size selectivity to maintain biodiversity: the effects of each exploitation pattern depend on the selectivity of the gear (i.e., the shape of the selection curve) relative to the available sizes. Catching a narrow range of species almost always reduced evenness and species richness more than taking the same catch from a broader range of species. In summary, neither selective nor nonselective fishing can be said to be gene...

Impacts of fishing gear on marine benthic habitats

Fishing affects seabed habitats worldwide. However, these impacts are not uniform and are affected by the spatial and temporal distribution of fishing effort, and vary with the habitat type and environment in which they occur. Different fishing methodologies vary in the degree to which they affect the seabed. Towed bottom fishing gears and hydraulic harvesting devices re-suspend the upper layers of the sedimentary habitat and hence re-mobilize contaminants and fine particulate matter into the water column. The ecological significance of these fishing effects has not yet been determined. Structurally complex habitats (e.g. seagrass meadows, biogenic reefs) and those that are relatively undisturbed by natural perturbations (e.g. deep-water mud substrata) are more adversely affected by fishing than unconsolidated sediment habitats that occur in shallow coastal waters. Structurally complex and stable habitats also have the longest recovery trajectories in terms of the re-colonization of the habitat by the associated fauna. Comparative studies of areas of the sea bed that have experienced different levels of fishing activity demonstrate that chronic fishing disturbance leads to the removal of high-biomass species that are composed mostly of emergent seabed organisms. These organisms increase the topographic complexity of the seabed and have been shown to provide shelter for juvenile fishes, reducing their vulnerability to predation. Conversely, small-bodied organisms, such as polychaete worms and scavengers, dominate heavily fished areas. Such a change in habitat may lead to changes in the composition of the resident fish fauna. Fishing also has indirect effects on habitat through the removal of predators that control bio-engineering organisms such as algal-grazing urchins on coral reefs. However, such effects are only manifested in those systems in which the linkages between the main trophic levels are confined to less than ten species. Management regimes that aim to incorporate both fisheries and habitat conservation objectives can be achieved through the appropriate use of a number of approaches, including total and partial exclusion of towed bottom fishing gears, and seasonal and rotational closure techniques. Different management regimes can only be formulated and tested once objectives and criteria for seabed habitats have been defined.

A Century of Fishing and Fish Fluctuations in Narragansett Bay

Fish and shellfish abundance for Narragansett Bay and coastal Rhode Island waters from landing data and surveys were compared over the past century using the originally abundant species. The first quantitative data became available in the late 1800s as conflicts developed between the hook-and-line fishermen and the fish trap fishermen with the hook-and-line fishermen claiming a reduction in the availability of fish. Subsequent data were available from the state of Rhode Island and National Marine Fisheries Service landing data, and from the Graduate School of Oceanography and Rhode Island Department of Environmental Management surveys. In the early records, several anadromous fish species were abundant which are no longer abundant or not reported in recent surveys such as alewife, shad, and smelt. Changes in shellfish include the disappearance of soft-shell clam, cultured oyster, and scallop and a replacement by quahog although the landing of quahog is recently down. Lobster was abundant in the early record and has increased in abundance in the recent records. Several species of fish that once dominated the catch have decreased. Boreal species like winter flounder have decreased with increasing water temperatures over the past 30 years. Migratory fish like menhaden and food fish like scup have decreased to low levels in the late 1900s compared to the 1800s. Predictions of fish yield from primary production indicate that migratory populations sustained the fishery in die late 1800s but in the late 1900s these populations no longer exist to sustain such a fishery. Survey data indicate these waters without fish have become prime habitat for crabs and lobsters.The legislatures of Massachusetts and Rhode Island, in 1869–1870 requested a law be passed prohibiting fixed apparatus for catching fish. (Spencer F. Baird, 1873).The compelling argument is not regulation and terse fact; rather we must accept our responsibilities and obligations, as users and temporary proprietors of the coastal commons, to keep track of what is happening there, to measure changes as they occur both naturally and. in response to our presence, and to act responsibly—all this because we, too, are pan of nature. It follows, than, that planning, restoration, and overall responsibility can and should, become part of our existence. How well we are progressing is the job of monitoring. (H. Perry Jeffries et al., 1988)

A multispecies age-structured assessment model for the Gulf of Alaska

Predation is the largest source of mortality for marine fish and may be an important process in regulating population size. Recent population models have attempted to quantify predation separately from other sources of natural mortality. Building upon such work, a multispecies age-structured assessment model (MSASA) for the Gulf of Alaska was developed, which included arrowtooth flounder (Atheresthes stomias), Pacific cod (Gadus macrocephalus), and walleye pollock (Theragra chalcogramma). Predation mortality was a flexible function of predator and prey abundances that was fitted to stomach-content data. A proof of concept illustration is presented here, assessing model outputs against a set of single-species models. The MSASA model was able to successfully estimate predation between species and integrate it into total mortality. Significant predation occurred on younger pollock and flounder. Results indicate a significant change in predation over time on pollock as a function of increased arrowtooth floun...

Using AMOEBAs to display multispecies, multifleet fisheries advice

In multispecies fish communities, predation levels change dynamically in response to changes in the abundance of predator and prey species, as influenced by the fisheries that exploit them. In addition to community-level metrics, it remains necessary to track the abundance of each species relative to its biological reference point. In situations with many interacting species, exploited by multiple fishing fleets, it can be complicated to illustrate how the effort of each fleet will affect the abundance of each species. We have adapted the AMOEBA approach to graph the reference levels of multiple interacting species exploited by multiple fleets. This method is illustrated with 10 species and eight fishing fleets in the North Sea. We fit a relatively simple response-surface model to the predictions of a fully age-structured multispecies model. The response-surface model links the AMOEBA for fishing effort to separate AMOEBAs for spawning stock biomass, fishing mortality, and yield. Ordination is used to give the shape of the AMOEBAs functional meaning by relating fish species to the fleets that catch them. The aim is to present the results of dynamic multispecies models in a format that can be readily understood by decision makers. Interactive versions of the AMOEBAs can be used to identify desirable combinations of effort levels and to test the compatibility of the set of single-species biological reference points.

Global analysis of depletion and recovery of seabed biota after bottom trawling disturbance

Significance Bottom trawling is the most widespread source of physical disturbance to the world’s seabed. Predictions of trawling impacts are needed to underpin risk assessment, and they are relevant for the fishing industry, conservation, management, and certification bodies. We estimate depletion and recovery of seabed biota after trawling by fitting models to data from a global data compilation. Trawl gears removed 6–41% of faunal biomass per pass, and recovery times posttrawling were 1.9–6.4 y depending on fisheries and environmental context. These results allow the estimation of trawling impacts on unprecedented spatial scales and for data poor fisheries and enable an objective analysis of tradeoffs between harvesting fish and the wider ecosystem effects of such activities. Bottom trawling is the most widespread human activity affecting seabed habitats. Here, we collate all available data for experimental and comparative studies of trawling impacts on whole communities of seabed macroinvertebrates on sedimentary habitats and develop widely applicable methods to estimate depletion and recovery rates of biota after trawling. Depletion of biota and trawl penetration into the seabed are highly correlated. Otter trawls caused the least depletion, removing 6% of biota per pass and penetrating the seabed on average down to 2.4 cm, whereas hydraulic dredges caused the most depletion, removing 41% of biota and penetrating the seabed on average 16.1 cm. Median recovery times posttrawling (from 50 to 95% of unimpacted biomass) ranged between 1.9 and 6.4 y. By accounting for the effects of penetration depth, environmental variation, and uncertainty, the models explained much of the variability of depletion and recovery estimates from single studies. Coupled with large-scale, high-resolution maps of trawling frequency and habitat, our estimates of depletion and recovery rates enable the assessment of trawling impacts on unprecedented spatial scales.