Spring 2023

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)


Moss Landing Marine Laboratories


The Mediterranean Sea has a long history of fishing exploitation that has led to a decline in the populations of many fish species. In order to preserve fish stocks and fishing interests, marine protected areas (MPAs) were established in some areas in the late 1970s. Studies have shown that where no-take areas have been enforced, they have resulted in greater abundance, body size, biomass, and diversity of commercially harvested fish species.

The Cap de Creus Natural Park in Girona, Spain was established in 1998. The park is divided into three management zones: a park zone, a partial reserve, and an integral reserve. Currently, information on fish distribution and habitats is limited; additional information is required to better evaluate the effectiveness of this MPA. The aim of my thesis project is to improve our understanding of the distribution, abundance, and size composition of fishes in Cap de Creus Natural Park.

This project consisted of three objectives: 1) To determine the differences in fish communities along a depth gradient in Cap de Creus Natural Park. I predicted that relative abundance, species diversity, species richness, community composition, and average length of conspecifics would shift across a depth gradient, with trends dependent upon species. 2) To determine how fish assemblages vary in relation to location and habitat factors in Cap de Creus Natural Park. I predicted that assemblage structure, abundance, and diversity would vary by habitat types and between northern and southern sites. 3) To determine the differences in fish assemblages among marine protection zones (Park zone, and reserve/ integral reserve) in Cap de Creus Natural Park. I hypothesized that relative abundance of fished species, especially those at higher trophic levels, would be higher inside reserve areas.

To accomplish these objectives, I surveyed 11 sites across the 3 levels of protection in the park in July 2018. I utilized several video survey methods to complete my objectives, including a baited lander (BRUV), diver-operated video (SCUBA), and two unbaited landers (Landers). I conducted these surveys mainly from 5 to 40 meters depth.

I observed more than 40 fish species across this survey. Overall, many species exhibited differences in their distributions and abundances by depth. Furthermore, community composition, richness, and diversity all differed above and below a depth of 25 meters. I also recorded differences in community composition among sampling sites grouped by protection level. In particular the fish community at site 5, located at Massa d’Or Island, differed from that at site 4, the location of the integral reserve. These differences were driven by higher abundances of vulnerable species at site 5. There were no apparent trends in species on the northern versus the southern side of the Cap de Creus peninsula. While the abundances of some species were correlated to habitat factors, further investigation is required to elucidate these relationships. Communities differed between reserve and open areas in term of richness for both SCUBA and Landers and in terms of Shannon diversity for SCUBA samples. Vulnerable species were most abundant at less than 25 meters depth. Highly vulnerable species were almost entirely confined to reserve areas that prohibited spearfishing. SCUBA surveys did not detect differences in the abundance of moderately vulnerable species between reserve and open areas. However, several moderately vulnerable species, D. sargus, S. cantharus, and D. puntazzo (with the exception of 1 observation in an open area), were only observed with Landers in reserve areas. The total abundance of spearfished species was higher inside reserve areas for Lander samples, but not for SCUBA samples. These differences in spearfished species abundance between tools can likely be attributed to differences in the three aforementioned moderately vulnerable species.

Further investigation is required to determine species-specific differences among tool types. However, a combination of BRUVs and diver-operated video surveys may improve monitoring of this MPA. It is difficult to make conclusions about the true effects of this MPA without baseline data, information from reference sites outside of the MPA, and long-term monitoring information. Moving the integral reserve to Massa d’Or Island or expanding the size of the integral reserve would certainly benefit highly vulnerable species in the park. Many MPAs, particularly in the Western Mediterranean, have shown positive effects on biomass of targeted species. Overall, most MPAs in the Mediterranean are still not well enforced, and large areas of the region remain unprotected. In order to best protect species, MPAs should be expanded and further management measures should be taken to limit the impacts of fishing in the region.