Fish & Fisheries

Fishing for Clues: Investigating Fisher Behavior in a Tropical Purse-Seine Fishery

August 15, 2013

Purse seine fishing. Photo: Robert K. Brigham/NOAA

This is the second essay in a three-part series featuring blogs by the student prize winners at the University of Queensland’s  Student Conference on Conservation Science, the first such conference held in Australia. The Nature Conservancy sponsored prizes for each winner, and asked each winner to submit an introduction to their research for Cool Green Science. Today, Tim Davies takes a look at how the behaviour of fishers affects marine conservation. –Eddie Game, conservation planning specialist

To help improve predictions of future fleet behaviour it is first necessary to develop an understanding of how fishers make decisions on how, where and when to fish. Photo: Tom Puchner under a Creative Commons license.
To help improve predictions of future fleet behaviour it is first necessary to develop an understanding of how fishers make decisions on how, where and when to fish. Photo: Tom Puchner under a Creative Commons license.

Fishing for clues: Investigating the behavior of fishers in a tropical tuna purse seine fishery

By Tim Davies, PhD candidate, Imperial College of London

The fish stocks of the world’s ocean are bountiful but not inexhaustible; as such we need to manage what we take and how we take it. It’s important to remember that the effective management of a fish stock is not so much about the fish as about the people trying to catch them.

There are many ways to regulate the activities of a fishing fleet, from modification of fishing gear to outright fishing bans. However, in implementing any of these measures it is important for managers to anticipate how the fleet is likely to behave in response.

Fishing is a commercial venture and fishers will invariably attempt to minimise the impact of management on themselves (and their profits). Where a response is misjudged – and management not designed appropriately – fishers may circumvent the measures intended to control their activity and management may be doomed to failure.

To help improve predictions of future fleet behavior it is first necessary to develop an understanding of how fishers make decisions on how, where and when to fish. In a study presented at the 2013 Student Conference on Conservation Science in Brisbane, Australia, I set out to understand the fishing behavior of a highly mobile, well-financed offshore fishery, using the western Indian Ocean tropical tuna purse seine fleet as a case study example.

I hypothesized that skippers will choose to fish in a particular area based on two ways of thinking; an area is considered “attractive” either because of prevailing conditions or known opportunities in the area (adaptive decision making) or from an expectation based on a fisher’s past experience of fishing in the area (heuristic decision making).

With these decision making approaches in mind I used a combination of statistical modelling of fishing patterns and qualitative interviews with skippers and other key experts to investigate how the tuna purse seine fleet behaved.

It was not an unexpected result that both decision making approaches were important in determining the behaviour of the fleet. However, each had influence at different spatial and temporal scales. Skippers had good knowledge of traditional fishing patterns that served as “rules-of-thumb” as where to search for tuna at any given time of year and the fleet followed long-running seasonal fishing patterns very closely.

However, these large traditional areas were approximate regions rather than specific fishing grounds and within these regions skippers tended to make greater use of adaptive decision making approaches.

This involved collecting fresh knowledge gleaned from information shared by other skippers and from remote data collected using technology (e.g. the location of fish aggregating devices or oceanographic conditions).

These results offer a new understanding of the behavior of tuna purse seine fleets in general but also carry implications for the management of the case study fishery. At a very broad level the location of fishing activity is governed by simple heuristics, with fishers moving between traditional areas. This behavior, based on what fishers have done in the past, is relatively stable and easy to predict.

However, management policies designed to affect large areas of ocean, such as closed areas or controls on certain fishing practices, would likely break established patterns of behavior and make adaptive decision making approach more important. This behavior is far more difficult to predict (even the fishers themselves may not know precisely what they will do next), particularly regarding how and where fishing effort might be reallocated. This sort of uncertainty is highly undesirable in fishery management.

This concern does not preclude the use of large-scale management in these situations, but it does highlight the need for careful consideration of what the potential outcomes of management of an offshore fishing fleet might be.

Tim Davies is now in the final year of his PhD at Imperial College London and is still enjoying himself. The study described here is an important part of his research as it provides the information needed for his ultimate research objective; developing a model that can predict the behaviour of the Indian Ocean tuna purse seine fishery. Tim started his PhD after becoming interested in the role of marine reserves in the open ocean. An important part of evaluating whether or not such marine reserves are likely to be effective is understanding how fishing fleets will respond.

Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.


Eddie Game

Eddie Game is the lead scientist for The Nature Conservancy, Asia Pacific Region. He is responsible for ensuring that the Conservancy remains a world leader in making science based conservation decisions, can robustly report on our impact, and that we get the greatest return for our conservation investments. Eddie has worked on conservation projects in over 15 countries, helping to apply innovative methods and analyses to projects as diverse as community protected areas in the Solomon Islands, grazing management in northern Kenya, and catchment restoration in Colombia. More from Eddie

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