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Ecology

Marine invertebrates- no backbone just makes them easier to eat.

The Paper: Tyler D. Eddy, Marta Coll, Elizabeth A. Fulton, and Heike K. Lotze. Trade-offs between invertebrate fisheries catches and ecosystem impacts in coastal New Zealand ICES J. Mar. Sci. (May/June 2015) 72 (5): 1380-138. doi: 10.1093/icesjms/fsv009.

 

Delicious lobster dinner. Credit: Benson Kua.

 

Introduction

invertfig

Invertebrate fisheries in New Zealand. (a) Number of invertebrate species or groups commercially harvested in New Zealand (Ministry for Primary Industries, 2014). Only invertebrate groups that are included in the Quota Management System are shown. (b) Reported landings of invertebrate groups commercially harvested in New Zealand (FAO, 2014).

The marine invertebrate seafood industry has been expanding- meaning more people happily dine on more species of crabs, lobsters, clams, scallops, squid and other spineless creatures. The well known threat of overexploitation in finfishing (typically just called fishing) is common and even expected but we have not yet heard about huge invertebrate fishery collapses.  Invertebrate fisheries remain largely unregulated risking overuse that could ultimately destroy the fishery as well as change the ecosystem as a whole through a chain reaction in the food chain.

One tool used to create effective management plans is modeling changes to certain fishery species and habitat over time.  These models can account for information such as habitat use, feeding habits and fishing pressures to create a prediction about how the population will change over time. In many places, not enough is known about the invertebrate fishery species to make accurate models.The authors chose to model New Zealand fisheries because of their available data on its invertebrate fisheries.

Methods

The researchers used a recently published model to investigate different exploitation rates of three invertebrate fisheries in New Zealand. They explored how changing the catch numbers of lobster, abalone and sea urchin affects the fishery and ecosystem.

Each simulation ran with the catch numbers of one species changing from 0% (unfished) to 100% (total depletion of stocks).  The model then predicted changes to the number of other animals in the area.  The aim of the study was to answer the three following questions:

  1. How many other types of animals at different levels in the food chain are impacted by changes in the rate of depletion of a fishery species?
  2. How do changes to the invertebrate numbers change the number of top predators?
  3. How does the biomass of different groups change?

Results and Significance

Increasing fishing of each of the three species increased the impacts on the rest of the ecosystem through changing the population numbers of other species, and lobster showed the most dramatic effects. Low depletion levels of each species created no ill effects but after >15% depletion of lobster and abalone or >10% depletion of urchin other animals were affected.

LODfig

Depletion ranges from 0 (no exploitation) to 100% (local extinction) and the present level of depletion (LOD) is indicated by the vertical line. Catch is shown as a proportion of maximum sustainable yield (MSY)

The model predicts for all three species that the current catch rate causes damage to the ecosystem and brings in animals at a rate that is not sustainable. Cutting the catch in half would maintain a sustainable fishery and minimize impacts on other species. If a  smaller catch was enforced, the model predicted greater catches in the future with larger economic rewards.

Responses were different for animals that live near the ground compared to open water species. Depletion of lobsters caused larger decreases for the open water community while abalone and urchin fishing caused larger problems for the ground species. Each of these animals consume different prey species and are victim to different predators. Shifting their numbers changes the numbers of other species in unique ways.

Modeling the potential impacts of invertebrate harvest allows us to create management plans to keep the fisheries strong. This study shows that invertebrate fisheries are connected to the rest of the ecosystem and can change the populations of animals at every level of the food chain. It also shows how different invertebrate species can impact the ecosystem in different ways. Just as we have overexploited finfish stocks, invertebrate species should not be overlooked because the threat to the ecosystem is just as serious.

 

What is your favorite invertebrate fishery species? What other creatures may be affected by harvesting that animal?

Discussion

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