Abstract
Community marine reserves are geographical areas closed to fishing activities, implemented and enforced by the same fishermen that fish around them. Their main objective is to recover commercial stocks of fish and invertebrates. While marine reserves have proven successful in many parts of the world, their success near important marine predator colonies, such as the California sea lion (Zalophus californianus) and the Pacific harbor seal (Phoca vitulina richardii), is yet to be analyzed. In response to the concerns expressed by local fishermen about the impact of the presence of pinnipeds on their communities’ marine reserves, we conducted underwater surveys around four islands in the Pacific west of the Baja California Peninsula: two without reserves (Todos Santos and San Roque); one with a recently established reserve (San Jeronimo); and, a fourth with reserves established eight years ago (Natividad). All these islands are subject to similar rates of exploitation by fishing cooperatives with exclusive rights. We estimated fish biomass and biodiversity in the seas around the islands, applying filters for potential California sea lion and harbor seal prey using known species from the literature. Generalized linear mixed models revealed that the age of the reserve has a significant positive effect on fish biomass, while the site (inside or outside of the reserve) did not, with a similar result found for the biomass of the prey of the California sea lion. Fish biodiversity was also higher around Natividad Island, while invertebrate biodiversity was higher around San Roque. These findings indicate that marine reserves increase overall fish diversity and biomass, despite the presence of top predators, even increasing the numbers of their potential prey. Community marine reserves may help to improve the resilience of marine mammals to climate-driven phenomena and maintain a healthy marine ecosystem for the benefit of both pinnipeds and fishermen.
Highlights
Marine reserves are geographic areas designated for the conservation and management of ecosystems and natural resources [1]
According to its Akaike Information Criterion (AIC) value, the best model uses the fish biomass as the response variable and both the level of protection of the site and the years since the marine reserve were established as explanatory variables (S1 Table)
The results show that the age of the marine reserve around the islands is a significant factor with a positive trend (p = 0.037), while the protection of the site was not (p = 0.694; S2 Table)
Summary
Marine reserves are geographic areas designated for the conservation and management of ecosystems and natural resources [1]. Proliferating around the world as an efficient and inexpensive way to maintain and manage fisheries while preserving biodiversity [2], they have proven successful in increasing fish biomass, organism size and diversity within their confines [2] They have been found to export recruits beyond their borders, even on a regional scale [3], and have been proven to increase ecosystem resilience to harmful conditions, such as climate driven hypoxia [4]. Local fishing cooperatives have exclusive rights to the marine resources around these islands, granted by an official concession from the Mexican government. On Todos Santos, which is close to a major urban center and fishing port [7], an aquaculture company operates fish enclosures in the southeast portion of the southernmost of these two islands
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