Fish in Space: Where the fish are, and why we need to know

Mobile trackingFish have to swim – and as a result, most fish are constantly on the move, some displaying very complex migration patterns over the course of their lifetimes. An article published earlier this year in the journal Environmental Monitoring and Assessment (Cooke et al. 2016) describes the essential value of spatial ecology to fisheries management and conservation. Spatial ecology is the study of how populations are distributed over different locations at given points in time, and the processes that influence those distributions – it’s actually a key part of the work we do at FISHBIO. Knowing where and when fish are present is central to identifying critical habitats, understanding how human activities influence fish populations, understanding interactions between species, and determining effective management strategies (Cooke et al. 2016). This seemingly basic information is often lacking for many species, the authors contend, and failure to account for fish spatial ecology can lead to ineffective management and biased assessments. Understanding spatial ecology can help develop and evaluate fisheries assessment protocols, support invasive species removals, describe habitat connectivity, improve habitat restoration measures, and understand how environmental factors (such as temperature and flow) affect fish populations.

Fish movements can be over meters or thousands of kilometers, and can change with the time of day or with the season. Knowing where fish aggregate or are likely to be present can help eradicate them, in the case of invasive species, sample them for research, or avoid them, in the case of reducing bycatch. Fishes may travel between different habitats for foraging or reproduction, and may have a choice of different routes to take. In California, researchers have studied the movement of juvenile salmonids through the maze of channels in the Sacramento–San Joaquin Delta to understand the factors that dictate which routes fish select as they migrate downstream. By understanding this selection process, managers can modify their actions to increase salmon survival, such as blocking or opening up channels at various junctures (like the Delta Cross Channel and Head of the Old River Barrier).

Historically, it was difficult to study spatial ecology, and studies often required following individual fish continuously or setting up long-term mark-recapture projects to figure out when and where fish were moving. This changed with the development of electronic tags (e.g., radio, acoustic, satellite, and passive integrated transponder (PIT) tags) that allow researchers to track the movements of individual fish in remarkable detail. Some advanced satellite tags can even provide information on a fish’s latitude, longitude, depth, environmental temperature, and acceleration forces. PIT tags are now as small as a grain of rice, and self-powered acoustic transmitters are being developed that obtain energy from the movement of the fish, so they don’t require batteries. Hydroacoustic technology has also excelled, like the high-resolution ARIS sonar camera that can be used to count and observe fish in real time without touching them. This kind of remote tool is especially useful for surveying sensitive, large-bodied endangered species, such as green sturgeon (Mora et al. 2015). At the other end of the size scale, the SmeltCam has been developed as a hands-off alternative to trawling for delta and longfin smelt (Feyrer et al. 2013). FISHBIO has embraced many of these tools in our work in California.

Developers have made numerous exciting advancements in technology for spatial ecology, yet their expense and training requirements have limited their application in developing countries, many of which are just starting to develop fisheries assessment plans. It may seem like putting the cart before the horse to conduct advanced biotelemetry studies in a region that lacks basic fisheries monitoring programs; however, the authors of the paper caution that first understanding fish spatial ecology is essential to develop an effective assessment program. Managers need to consider when and where to survey fish, and tools such as the ARIS and biotelemetry can inform how standardized monitoring programs are implemented. One of FISHBIO’s primary goals working in the Mekong region is to draw on the technical expertise developed in the United States to build capacity for similar research in the Mekong basin. Cooke and colleagues urge that despite the cost of using these advanced tools, “the ecological costs of not studying the spatial ecology of a population may be much greater – both in terms of economics and conservation.” We couldn’t agree more.

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