Marine Reserves, Unexpected Effects

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Marine reserves have been of interest since the first months of this blog in 2011 and are still a mainstay of our incoming and outgoing newsfeeds. Much of our recent interest in the intersection between marine biology and conservation has been focused on invasive species since 2013, due to the super series penned by Phil Karp, most recently added to last week. Thanks to Jason G. Goldman and Conservation for this summary of a special topic within this intersection:

Most marine reserves are optimized for reef fish. These are fish that are born, live, reproduce, and ultimately die in a small area – sometimes on just a single reef. Where there is connectivity across a large area, it’s usually while the fish is in its larval stage. Once it matures, it stays put.

It’s a fitting strategy for conserving fish that live on coral reefs, rocky reefs, or in kelp forests, but does it do much to help those species that are more migratory? These are animals, like the Gulf of Mexico’s gag grouper, that spend their childhoods in one place, a nursery habitat like a mangrove, estuary, or kelp forest, and then migrate to live out their adult years in an adult habitat, like a reef or along the continental shelf.

What would a marine reserve optimized for these migratory species look like, at least in theory? That’s the question that University of North Carolina, Wilmington marine biologist J. Wilson White took up in a recent issue of the journal Biology Letters.

He started by using a mathematical model to describe a theoretical population of fishes that spend some amount of time in a nursery before migrating to an adult habitat after maturation. He simplified his model by restricting maturing juveniles from a given nursery to migrate to its own paired adult habitat. However, mature adults could move about between individual adult habitats in some cases.

White then subjected his theoretical fishes to the pressures of three different types of theoretical fishing. Under one regime, the fishery targeted only the adult habitat. Under a second regime, the fishery targeted only the nursery. Under the third, the fishery targeted both habitats. Each theoretical fishing regime was simulated both with and without reserves.

He found in most cases that reserves were critical for maintaining fisheries at sustainable levels. In other words, they were necessary to guard against overexploitation.

When fishing was allowed in the adult habitat, White’s model mimicked the “reef fish” model. Instituting reserves allowed the fish to be harvested at a high yield; without reserves, the fishery collapsed. However, the fishery collapsed even at high yields in the adults had high levels of connectivity between adult habitats. Reserves were only useful when the adults didn’t move around all that much…making them, in some ways, just like reef fish…

Read the whole summary here.

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