Invertebrate Fisheries are Growing, but Often Poorly Understood
Studies suggest a need for careful management, similar to forage fish
Lobster, shrimp, squid, crabs, and other invertebrates are increasingly important to the world’s supply of seafood, but managers often lack the information needed to ensure the catch is sustainable. Now, a series of studies has revealed for the first time that invertebrates are as important to marine ecosystems as forage fish, a group widely recognized as critical food for larger-bodied species. The studies also have found that invertebrates may be more vulnerable to fishing than forage fish, suggesting the need for reduced catch in some locations.
The studies were led by Tyler Eddy and Heike Lotze of Dalhousie University and supported by the Lenfest Ocean Program.
More fishing, without more data
As the global catch of wild finfish has declined, marine invertebrate fisheries have emerged in many places. Since the 1950s, their catch has increased six-fold, and the number of species targeted has doubled. Lobster is now the top seafood export by value in Canada and New Zealand, and six invertebrates are in the top 10 U.S. seafood species by landed value. Invertebrates are also potentially important to ecosystems, as predators, competitors, and prey.
Population change is often poorly understood for invertebrate species, in part because it can be difficult to measure abundance and the age of individuals. Furthermore, many of these fisheries lack formal management plans.
Three studies published between 2015 and 2017 suggest it is urgent to improve management of invertebrate fisheries and provide guidance on how to do so. The most recent and far reaching of these studies (Eddy et al. 2017) looked at 12 ecosystems around the world using simulation models. These models draw on real-world data to forecast the outcomes of various options for managing invertebrate fisheries.
Invertebrates are sensitive to fishing and important in many ecosystems
One result of the 2017 paper was that most invertebrate groups are highly sensitive to fishing. On average, an invertebrate population reaches its highest catch relative to maximum sustainable yield (MSY) when its population is depleted by about 45 percent relative to its unfished biomass. MSY is a common fishery benchmark, denoting the level of fishing mortality that, if exceeded, will result in long-term decline. By contrast, forage fish were less sensitive to fishing, producing MSY when depleted by 65 percent (Figure 1).
Figure 1. Comparing Invertebrate and Forage Fisheries
The researchers also simulated the impacts of invertebrate fisheries on other species in the ecosystem. To do this, they simulated fishing (or bycatch) of several invertebrate groups separately. For each group, they reduced its abundance to 40 percent of the unfished maximum. Then they measured the proportion of the other species (or groupings of species) in the ecosystem whose abundance changed by at least 40 percent (Figure 2). According to this metric, the ecosystem impacts of invertebrate fisheries were comparable to the impacts of forage fish fisheries. Fisheries for cephalopods (squids and octopuses) showed the strongest impacts.
Figure 2. Ecosystem Impact of 9 Invertebrate Groups
In addition, the 2017 study found that reducing fishing to allow invertebrates to remain at 75 percent of unfished abundance could be a win-win strategy, providing 90 percent of the maximum yield while reducing impacts on other species.
Spotlight on New Zealand and Canada
These findings were borne out in specific places by two other papers (Eddy et al. 2016, Eddy et al. 2015), which focused on the Cook Strait of New Zealand and the western Scotian Shelf of Nova Scotia, Canada.
These papers found that fishing for invertebrates is at historically high and often unsustainable levels in both places. The effects of invertebrate fisheries on non-target species were significant in many of the simulations, suggesting that fishing could lead to ecosystem changes not accounted for under current management. For example, lobster fishing in New Zealand appeared to increase the abundance of several other predators, including some fishes, birds, and other invertebrates, possibly because lobsters compete with them for food. On the other hand, it reduced the abundance of sea cucumbers, sponges, and other sessile species, through some ripple effects that are not yet clear.
The authors highlighted two key implications of their work. First, they urge managers to consider the ecological consequences of invertebrate fisheries. As with forage fish, failure to account for ecosystem effects could have unintended consequences for other fisheries and for vulnerable species. Second, they recommend managers consider tighter restrictions on fishing for invertebrates, since they appear to be more sensitive to fishing than forage fish, on average.
Eddy, T. D., Lotze, H. K., Fulton, E. A., Coll, M., Ainsworth, C. H., de Araújo, J. N., Bulman, C. M., Bundy, A., Christensen, V., Field, J. C., Gribble, N. A., Hasan, M., Mackinson, S. and Townsend, H. (2017). Ecosystem effects of invertebrate fisheries. Fish and Fisheries, 18, 40–53. doi: 10.1111/faf.12165
Eddy, T. D., Araújo, J. N., Bundy, A., Fulton, E. A., & Lotze, H. K. (2016). Effectiveness of lobster fisheries management in New Zealand and Nova Scotia from multi-species and ecosystem perspectives. ICES Journal of Marine Science, 74(1), 146-157. doi:10.1093/icesjms/fsw127
Eddy, T. D., Coll, M., Fulton, E. A., & Lotze, H. K. (2015). Trade-offs between invertebrate fisheries catches and ecosystem impacts in coastal New Zealand. ICES Journal of Marine Science, 72(5), 1380-1388. doi: 10.1093/icesjms/fsv009