Editor’s note: In 2016, roughly one-third of the total value of the world’s trade of fish and fish products was invertebrates. (They were approximately one-fifth of the global fish trade by live weight.) To learn more about the state and future of invertebrate fisheries management, The Skimmer interviewed Heike Lotze, a professor in the Department of Biology at Dalhousie University in Halifax, Canada. In this interview, we discuss several of her papers published over the past decade on the recent expansion, ecosystem effects, and management of invertebrate fisheries, including a recent synthesis “Ecosystem effects of invertebrate fisheries” published in Fish and Fisheries in 2017.
The Skimmer: As global catch of invertebrates increases, what impacts are invertebrate fisheries having on marine ecosystems?
Lotze: Invertebrate catches have increased more than six-fold globally since the 1950s. Catches include all major species groups – from lobster, shrimp, and crabs (crustaceans) to octopus, cuttlefish and squid (cephalopods) to mussels and snails (mollusks) to sea urchins and sea cucumbers (echinoderms). In many countries, invertebrates are some of the most lucrative commercial fisheries and provide coastal communities with valuable livelihoods and associated benefits. The global increase in catches has been accompanied by the spatial expansion of invertebrate fisheries: many more countries are engaging in fishing invertebrates, and many more areas within countries are now fishing invertebrates. For example, sea urchin and sea cucumber are now fished around the globe, and fishing for invertebrates has expanded from shallow to deeper waters to maintain or enhance catch levels. Fisheries have further shifted from large- to smaller-sized individuals and from high- to lesser-valued species, usually in response to declining catches and following a ‘fishing down the value-chain’ pattern.
Many people may think it is ‘just’ invertebrates, but these species play important ecological roles in marine ecosystems. These roles are often more diverse than the roles that fish play, consequently the impacts of invertebrate fisheries on other species and marine ecosystems are more varied than those of finfish fisheries. For example:
- Many invertebrates are important prey for higher trophic level species, such as fish, whales, turtles, and seabirds, and reducing invertebrate abundance can have ripple effects through marine food webs, comparable to those of forage fish;
- Many mussels, oysters, and sponges enhance biodiversity by creating three-dimensional structures that are important habitat for other species – for settlement, finding food, finding shelter, breeding, and nursery grounds;
- Many invertebrates filter feed which improves water quality and clarity and provides benefits to other organisms, including humans;
- Herbivore grazers, such as many urchins and gastropods, act as lawn mowers keeping algal carpets in check; and
- Detritivore sea stars and sea cucumbers clean up ocean floors as the scavengers of the sea.