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Protecting Well-Traveled Fishes: A New Approach


Breen, P., P. Posen, and D. Righton. 2015. Temperate Marine Protected Areas and highly mobile fish: A Review. Oceans and Coastal Management, 105: 75-83. doi:10.1016/j.ocecoaman.2014.12.021

Marine Protected Areas

Fisheries managers have been developing a new approach to protecting the vital resources of our oceans over the last decade: ecosystem-based management, which focuses on protecting the ecosystem of a given area rather than individual fish species. Traditionally, governments have attempted to protect individual fish species and stocks by drafting rules and regulations specific to each type of fish. This results in many slightly different rules across local, state, and federal levels, multiplied across many different species of fish. Unfortunately, a fisherman operating within the legal rules of fishing for one particular species often has some impact on the other organisms in the area, either in the form of bycatch or habitat disturbance. Ecosystem-based management fixes this inefficient system and seeks to protect as many species as possible. Probably the best and most successful example of ecosystem-based management is the use of Marine Protected Areas (MPAs).

Many tropical reef fish, like this clown fish, never leave their small territory, making them relatively easy to protect with MPAs

Many tropical reef fish, like this clown fish, never leave their small territory, making them relatively easy to protect with MPAs

In creating MPAs, managers essentially draw a box around an aquatic environment and say “this entire area is now protected.” MPAs can employ different degrees of protection from no boats or fishing allowed to boats and fishing allowed, but only with certain methods like hook-and-line. MPAs have been incredibly successful with certain types of marine environments like coral reefs because, conveniently, the corals and the associated species don’t move very much. Therefore, managers can designate the reef as a protected area and effectively protect most, if not all, of its inhabitants.


This is great news, but the majority of fish species that are commercially and ecologically valuable, particularly in the U.S., are not reef fish. In fact, many of our most valuable species fit into a category of fish known as Highly Mobile Fish Species (HMFS) – fish that tend to travel long distances on a regular basis.

Highly Mobile Fish Species (HMFS)

As many as 200-300 species of fish make large scale migrations on a regular basis in order to improve their survival. Fish in non-tropical regions are more likely to be more mobile due to greater seasonality of their environments. A major reason fish will migrate is to spawn; they go where their offspring will have a greater chance of survival, usually because of decreased predation risk.

The migration route of one bluefin tuna in one year

The migration route of one bluefin tuna in one year

Commercially valuable species like cod and tuna, apex predators like large sharks, and forage fish like herring all fall into the HMFS category. In the case of tuna, bill fish, and many large sharks, these fish are so mobile that an individual fish may swim around the entire globe in a given year. It’s impossible to draw a protective box around the entire world’s oceans to protect fish like this. So, how do we protect our most valuable fish species if we can’t keep them in an MPA?


The Study

Breen et al. conducted a review to gather all of the published scientific literature available for Marine Protected Areas and Highly Mobile Fish Species. Their goal was to determine if there is any evidence that MPAs are helpful to HMFS. In doing so, the authors attempted to identify problems with existing approaches and find ways we may be able to improve our management of HMFS. This study focused on MPAs in temperate waters and ignored tropical and reef-associated MPAs.

Important Findings

Figure 2 - A Pacific salmon spawning migration

A Pacific salmon spawning migration where fish are densely concentrated in a river.

Breen et al. found evidence that we do not need to protect the entire range of the entire life history of a species in order to successfully protect it. Rather, a network of smaller MPAs strategically positioned in geographic locations during the time of year that fish aggregate in these smaller regions can go a long way towards protecting them. For example, when species like diadromous fish move from being widely dispersed in the open ocean to heavily concentrated in the river where they spawn, they make themselves much more vulnerable to exploitation. The authors suggest that we must identify the locations and times of year that fish are most vulnerable and protect these areas. Following this approach, a network of several smaller key areas can be protected, potentially over short spans of time, and yet still provide adequate protection for important HMFS.

A Call for Telemetry!

Figure 3 - A satellite GPS telemetry tag attached to the dorsal fin of a great white shark (ocearch.org)

A satellite GPS telemetry tag attached to the top of the dorsal fin of a great white shark. After release, the movements of the tagged sharks can be followed at ocearch.org

If we want to protect HMFS by accurately identifying their movement patterns and what habitats they use during different times of the year, then we need to be able to track the movements of individual fish. That is where telemetry comes in. Telemetry is a technique used by scientists to track animal movements by placing a transmitter tag on the animal and detecting its transmissions in order to locate the animal over time. With telemetry data, we can determine when a population migrates, if fish are spread out over a wide section of ocean, if spawning happens in one small concentrated region, and find potential “fish highways” of fish travel along a tightly defined route. This is the kind of information that Breen et al. identified as necessary in order to design effective MPAs for HMFS.


With enough telemetry data, HMFS will be effectively protected with MPAs, right? Well, it’s not quite that simple. There are a number of challenges that surround MPAs designed to protect HMFS. For example, a highly mobile predator forages where the prey are, not necessarily in a set geographic location. Generally, big fish follow little fish, which follow plankton, whose abundance in an area depends on temperature, sunlight, currents, winds, and many other factors. Unfortunately, legislation doesn’t move as fast as these factors shift, making it potentially difficult to define important areas to protect. Another problem with drafting legislation to protect HMFS is the fact that many HMFS do not recognize national boundaries. They may forage in the national waters of one country, and spawn in the national waters of another. In the case of large sharks and tuna, their habitats include nations on opposite sides of the world, as well as international waters. International groups like the International Union for the Conservation of Nature (IUCN) and the Convention on Biological Diversity (CBD) can help to facilitate the design of MPAs for well-traveled species.

The greatest challenge to this study and consequently to the creation of future MPAs designed to protect HMFS is a lack of data. And not just the lack of detailed telemetry data. Breen et al. attempted to identify what aspects of certain MPAs work well for temperate HMFS and what features aren’t as beneficial. The problem is: there aren’t very many temperate MPAs, and even fewer that have any relevance to HMFS. In order to better understand what works and what doesn’t, we need to be comfortable with the fact that our earliest attempts at designing MPAs for HMFS may not be terribly successful, but recognize that we can learn and adapt our techniques to better protect these vital species in the future.


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