Authors: Kailin Kroetz, James N. Sanchirico, Matthew N. Reimer, Jamie Ashander

Anyone who has seen a food web of a marine ecosystem has seen a model in which little fish eat plankton, medium-sized fish eat little fish, and the biggest fish eat everything else. A food web is a familiar way to conceptualize the ecological connectivity of marine species. In a paper titled “Defining the Economic Scope for Ecosystem-Based Fishery Management”, and published this year in Proceedings of the National Academy of Sciences, we pose and examine the question: could a parallel model be used to conceptualize economic connectivity and explore the management implications of policy choices?

We use the commercially significant and ecologically vibrant marine fisheries of Alaska as an example to show how economic connections between fisheries can result in unintended consequences from fisheries policies. This type of visual representation could be an important tool within the new management paradigm of Ecosystem-Based Fishery Management (EBFM), which aims to design policies that consider fishery connectivity.

To address the challenge of how to represent economic connectivity of fisheries, we use a detailed, 24-year dataset of fishing vessels (about 6,000 to 8,000 per year) that participated in 104 Alaska fisheries between 1991 and 2015. In Figure 1, we use data on participation of these fishing vessels to visually represent one form of economic connectivity in fisheries.

Fig 1: Economic connectivity (cross-fishery participation) of Alaska fisheries from 1991 to 2015. Fisheries that had catch shares by 2015 are squares, which are bordered in red after catch share implementation. Nodes represent fisheries with node size and color scaling with the number of active participants in the fishery. Edges represent cross-fishery participation and scale with the number of joint participants in each of the two fisheries an edge connects.

Economic connectivity of fisheries can occur if fishers consider more than one fishery when deciding where, when, how to fish, and how much fish to catch. If connectivity exists, there is a potential for economic, and in turn, ecological outcomes in multiple fisheries to be jointly determined. It follows that impacts from a management change in one fishery may therefore “spill over” into other fisheries.

To study this type of interaction, we test whether changes in economic connectivity in the Alaska fisheries network coincide with the implementation of each of six main catch share programs. Catch shares are a form of management that allocate shares of an annual harvest cap to fishers in the form of harvesting rights.

Catch shares are a valuable policy tool to explore economic connectivity for three primary reasons. First, catch share programs are increasingly used worldwide–over 150 catch shares are implemented globally, especially in commercially important fisheries, of which about two dozen exist in the United States— and are therefore an important policy to explore from a management perspective. Second, catch shares tend to be implemented and evaluated on a single-fishery basis, in direct contrast to EBFM’s ecosystem scale. Third, many catch share programs specifically aim to address excess participation (or overcapacity) in a target fishery—namely, the fact that there may be too many boats or too many fishers going after the same kind of fish at the same time and place.

All of these factors raise the question: If catch shares are introduced to a fishery, where does that excess participation go?

The best way to conceptualize this potential “spillover” from a catch share program is to focus on the reactions by the fishers of the target fishery. The participants may change their fishing effort by participating in different fisheries or by reallocating effort (for example, the number of days fished) between fisheries. In this context, when fishers change effort in a “non-target” fishery in response to a policy that is implemented in a target fishery, “spillover” of policy impacts beyond the target fishery is said to occur. This reallocation of effort by fishers may be viewed as positive or negative. On one hand, reallocating effort may keep fishers fishing and or help fishers maintain a diverse catch portfolio, two outcomes often viewed as desirable for small-scale fishers and fishers from more remote communities. On the other hand, increasing participants and potentially effort in fisheries beyond the target fishery can lead to additional fishing pressure on the stock which can result in negative ecological impacts and/or erode the profitability of the other fisheries.

The paper provides empirical evidence that the implementation of catch share programs is associated with significant changes in non-catch share fishery participation and network connectivity. These significant changes coincide with some, but not all, catch share programs. Importantly, the extent to which impacts from catch shares spill over into other fisheries will depend on both the nature of the catch share program and the regulatory environment of other fisheries. \link{Figure 1} shows the data analyzed in the paper, illustrating how economic connectivity has changed over time and how some changes coincide with implementation of catch share program.

This work suggests that fisheries managers should seriously consider economic connectivity and the potential for spillover when designing and evaluating fishery policies—and gives them a powerful tool to better understand such consequences.