Too many fish, too few hooks: examining bias in hook-and-line surveys

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Scientific surveys using fishing rods, each fishing multiple hooks, have the advantage of being able to access rocky areas while obtaining samples of fish for length and age estimation. However, in areas with lots of fish, it is possible for nearly every hook to catch a fish, resulting in an upper limit on the number of fish that can be counted. This problem of hook saturation can lead to catch rates not directly matching trends in fish abundance in the area being surveyed. A new simulation study delves into this problem, finding that catch rates do indeed decline more slowly than abundance for hook-and-line surveys, and that surveys targeting sites with higher densities of fish are able to better track changes in abundance. In addition, competition for hooks among species can lead to bias when one of the species more aggressively attacks baited hooks. Nevertheless, hook-and-line surveys fill a vital role in assessing the status of species that cannot be surveyed by other methods. The research was conducted by recently-graduated SAFS PhD student Peter Kuriyama, SAFS professor Trevor Branch, Allan Hicks of the International Pacific Halibut Commission, and John Harms and Owen Hamel at NOAA Fisheries, and appears in the Canadian Journal of Fisheries and Aquatic Sciences.

Catch per hook (CPUE) declines more slowly than abundance across a variety of scenarios. As the number of sites fished increases, CPUE becomes more precise (smaller vertical lines indicating uncertainty), regardless of the way in which fish are distributed from area to area (rows of figures). In most scenarios, hook-and-line surveys are still able to detect declines in fish abundance (filled black surveys) unless the declines are small, few sites are surveyed, or fish are distributed in a very patchy fashion (white circles).

Fantastic beasts and where to find them

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New and weird species are being discovered all the time, and the latest is the Narungga Frogfish (Histiophryne narungga), which has just been described. The name honors the Narungga tribe of indigenous Australians who traditionally inhabited the lands in which it was found. The new species comes in a variety of dotted forms, occurs in southern and western Australia, and is a member of the order Lophiiformes. The new species is described in the journal Copeia by Rachel Arnold of the Salish Sea Research Center and SAFS emeritus professor Theodore Pietsch.

A collation of five images of Narungga Frogfish.

The three pillars of fisheries sustainability

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Fisheries management is often seen as a balancing act that aims for economic development, environmental protection and social development. Previous work shows that overfishing or other forms of poor ecological health, reduces economic profits; and it has long been assumed that pursuit of profits leads to poor social outcomes for fishing communities. But now a new analysis of 121 fisheries worldwide suggests this second assumption may not hold, based on scores of 68 different ecological, economic, and social metrics for each fishery. The results show that there is a positive link between all three of the pillars of fisheries sustainability, such that better profits lead to better social outcomes and better ecological protection, and that at worst, the three pillars are not correlated with each other. The positive correlations among the pillars are stronger with increased use of rights in fisheries management, with harvest rights showing the strongest correlations and open access the weakest. The new work by an international group of authors including SAFS professor Chris Anderson, appears in the journal PNAS.

Fisheries performance scores are positively related to each other for ecological, economic, and community (social) measures, and this holds for fisheries that are open access (green), have limited access (blue), or have fishing rights (red).

Newly discovered fish species: the Polkadot Dwarfgoby

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Oceanic discoveries of new species continue at pace, with a new species added to the 34,000 previously described: the Polkadot Dwarfgoby (Eviota maculosa). The new species occurs in New Guinea, Indonesia, and Pohnpei in the Federated States of Micronesia, and is distinguished by unique fin patterns, distinctive genetics, and multiple rows of trident-like teeth in both the upper and lower jaws. The formal description by David Greenfield of the California Academy of Sciences, SAFS professor Luke Tornabene, SAFS PhD student Marta Gómez-Buckley, and Mark Erdmann of Conservation International, was published in the Journal of the Ocean Science Foundation.

M.V. Erdmann
Polkadot dwarfgoby from Teluk Saleh, Sumbawa, Indonesia
L. Tornabene
Distinctive three-pointed (tricuspid) teeth in the lower jaw of the Polkadot Dwarfgoby.

Does more fish mean more money?

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Bristol Bay in Alaska hosts one of the world’s largest salmon fisheries every year, targeting bountiful runs of sockeye salmon. The fishery is managed using escapement goals that ensure sufficient salmon escape the fishery every year to spawn upriver. Recently, increased escapement goals were proposed for Bristol Bay that were intended to allow more salmon to spawn upriver, because of calculations suggesting this would lead to larger average catches. However, fishing communities and industry opposed this change, arguing that this would lead to more variable catches, and less predictable profits and tax revenues from fishing. A new economic analysis provides evidence to support this stance: increasing escapement would lead to more years with no or low catches, but in years with high salmon runs, catches would not increase much because processors lack the capacity to handle large salmon runs in Bristol Bay. The net effect would be more fish but not necessarily higher profits. Furthermore, parts of the salmon industry that are tied to a specific fishing district, and that use small boats or set-nets, would be more vulnerable since they would be less able to shift fishing to a different district during more frequent years of low catches. The analysis shows the importance of modeling biological, social, and economic factors together before making changes to fisheries management rules. The authors of the paper that appears in the Canadian Journal of Fisheries and Aquatic Sciences are Jocelyn Wang (Economics, University of Washington), SAFS professors Chris Anderson and Ray Hilborn, Curry Cunningham of NOAA, and Michael Link of the Bristol Bay Science and Research Institute.

Small schooling fish require carefully tailored management to balance catches and collapse risks

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Forage fish are small, densely schooling fish at the heart of many marine ecosystems. These fish, including sardines, anchovies, menhaden and their kin, consume tremendous quantities of plankton and also provide abundant food for top marine predators such as larger fish and whales. A key characteristic of these species is their dramatic fluctuation in numbers between high “bonanza” periods and low “collapse” periods, which make them hard to manage. A new study now looks at which kinds of management rules offer the best trade-offs between high and stable catches and minimizing the risk of collapses. It turns out that aiming for stable catches results in more severe collapses, and that early detection of impending collapse is of great importance in averting bad outcomes in terms of catches and collapses. Furthermore, no single management rule was appropriate for all forage fish species. Instead, rules need to be tailored for each species individually. The new paper appears in the journal Fish and Fisheries and was authored by SAFS PhD student and current postdoc Margaret Siple, SAFS professor Timothy Essington, and CSIRO scientist Éva Plagányi.

The management strategy evaluation approach simulates both the management rule and the underlying changes in numbers of the fished population.

 

 

Rebuilding endangered species using a stepping-stone model for reintroduction

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Captive breeding programs are intended to rebuild highly endangered populations, but a major problem is how to reintroduce captive-bred individuals back to their native habitat. Often, there is low survival of reintroduced individuals compared to wild-born individuals. Such is the case for the critically endangered Vancouver Island marmot, which had shrunk to just 30 individuals in 2003. A new experiment compares survival to breeding age for three strategies: transferring wild-born individuals, translocating captive-born individuals to wild habitat, and a new stepping stone strategy that involved first transplanting captive born individuals to a safe wild area with high survival before transferring them in their second year to the lower-survival final destination. While the highest success is from transferring wild individuals to new areas, the stepping-stone approach was estimated with 83% certain to have higher probability of reaching prime breeding age than the straight-to-wild individuals. The new results, coauthored by SAFS professor Sarah Converse and new SAFS postdoc Nathan Hostetter, appear in the journal Animal Conservation.

Three translocation methods were compared for Vancouver Island marmots: from captivity to the wild area, from captivity to a safe wild area to the final wild area, and from the safe wild area to the final wild area.

Pinpointing the footprint of trawling fishing vessels on coastal shelves

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In recent years there has been a growing debate about what proportion of the oceans is fished, with estimates ranging from well above 50% to just 4%. A new paper now looks at one of the most widespread and damaging fishing types, trawling, where a net is dragged over the sea bottom to capture fish. The new method focuses on shallower continental shelves that are less than 1000 m in depth, finding that the trawling footprint varies hugely across regions from 0.4% of the area to more than 80%, with an average of 14% for all regions examined. The new work is highlighted in UW News and appears in the Proceedings of the National Academy of the USA. It was led by SAFS postdoctoral scholar, and includes SAFS professor Ray Hilborn among the more than 40 coauthors in the international collaboration.

Trawling intensity in different parts of the world.

A superensemble approach for managing data-limited fisheries

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Many fisheries around the world are not formally assessed, and for these fisheries it is hard to know whether they are overfished or not, and how much to fish to ensure that fishing remains sustainable. A suite of models has been developed that can be applied to fisheries where the only data available are time series of catches, but there is no information on trends in actual fish numbers. In a new study, these models are combined into a “superensemble” of models, in the same way that hurricane forecast models are combined to make predictions, and then tested with different types of rules for setting catches. The superensemble was able to reduce the risk of overfishing, but often resulted in very small catches, compared to continuing catches at current levels. In addition, when rules were based on controlling fishing effort, they were robust to errors in the data-limited catch-only models; but when rules were based on controlling fishing catches, this often resulted in depletion and overfishing. Thus the new superensemble approach offers another tool for better management of the many fisheries worldwide for which data collection is difficult and expensive. The paper is led by Jessica Walsh of Simon Fraser University, includes former SAFS postdoc Sean Anderson and current SAFS researcher Merrill Rudd as coauthors, and appears in the journal Fish and Fisheries.

Habitat preservation is a critical part of good ocean fisheries management

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Marine fisheries management aims to keep fish populations at sustainable levels while producing seafood. Fisheries that are assessed to be overfished must have their populations rebuilt to sustainable levels by reducing catches to lower levels. Usually the assessment of status relies on a complicated fisheries stock assessment model, sort of like a weather forecast for fisheries, that estimates the level of sustainable catch that can be taken from a fisheries population. But these models seldom take into account changes in fish habitat. A new paper now highlights the critical role that fish habitat plays in assessing the status of fisheries, noting that nearly half of assessed fisheries rely heavily on habitats that are degrading over time, such as seagrass, mangroves, coral reefs, and kelp forests. Since so many types of habitats are in decline, assessments of fisheries status must take this into account when trying to understand why some fish numbers are going down over time. The authors urge for a higher profile to be placed on protecting fisheries habitat in addition to controlling catches and other more traditional forms of marine fisheries management. The new paper led by Christopher Brown of Griffith University, Australia, includes SAFS professor Trevor Branch as a coauthor, and was published in the journal Fish and Fisheries.

Ways in which changes in habitat quality can affect a fish species that uses different habitats as it ages. Spawning habitat, refuge for baby fish, and anoxic areas will all affect the total population size and assessments of fish status.