Coral reef fishes exhibit beneficial phenotypes inside marine protected areas

Abstract

Human fishing effort is size-selective, preferentially removing the largest individuals from harvested stocks. Intensive, size-specific fishing mortality induces directional shifts in phenotypic frequencies towards the predominance of smaller and earlier-maturing individuals, which are among the primary causes of declining fish biomass. Fish that reproduce at smaller size and younger age produce fewer, smaller, and less viable larvae, severely reducing the reproductive capacity of harvested populations. Marine protected areas (MPAs) are extensively utilized in coral reefs for fisheries management, and are thought to mitigate the impacts of size-selective fishing mortality and supplement fished stocks through larval export. However, empirical evidence of disparities in fitness-relevant phenotypes between MPAs and adjacent fished reefs is necessary to validate this assertion. Here, we compare key life-history traits in three coral-reef fishes (Acanthurus nigrofuscus, Ctenochaetus striatus, and Parupeneus multifasciatus) between MPAs and fished reefs in the Philippines. Results of our analyses support previous hypotheses regarding the impacts of MPAs on phenotypic traits. Asymptotic length (Linf) and growth rates (K) differed between conspecifics in MPAs and fished reefs, with protected populations exhibiting phenotypes that are known to confer higher fecundity. Additionally, populations demonstrated increases in length at 50% maturity (L50) inside MPAs compared to adjacent areas, although age at 50% maturity (A50) did not appear to be impacted by MPA establishment. Shifts toward advantageous phenotypes were most common in the oldest and largest MPAs, but occurred in all of the MPAs examined. These results suggest that MPAs may provide protection against the impacts of size-selective harvest on life-history traits in coral-reef fishes.

Fig 1. Sites of MPAs and fished reefs where collections of three coral-reef resident fishes occurred.

Fig 2. Scatterplot of the length-at-age of A. nigrofuscus individuals caught inside and outside of the Bani, San Salvador, and Taklobo Farm MPAs in Masinloc, and associated Von Bertalanffy growth curves for protected and fished populations.

Fig 3. Scatterplot of the length-at-age of C. striatus individuals caught inside and outside of the Bani, San Salvador, and Taklobo Farm MPAs in Masinloc, and associated Von Bertalanffy growth curves for both protected and fished populations.

Fig 4. Scatterplot of the length-at-age of P. multifasciatus individuals caught inside and outside of the Bani and San Salvador MPAs in Masinloc, and associated Von Bertalanffy growth curves for both protected and fished populations.