Detection of protection benefits for predatory fishes depends on census methodology

Abstract

1. Marine protected areas (MPAs) are used as fisheries management and conservation tools. Well-enforced no-take zones allow the rebuilding of natural populations of exploited species; however, there is still controversy on the role of buffer zones.2. The effectiveness of MPAs could be underestimated, as fish population assessments depend largely on traditional methodologies that have difficulties in detecting predatory fish because of their low abundances, their patchy distribution, and their reaction to the presence of divers.

Using complementary visual approaches to investigate residency, site fidelity and movement patterns of the dusky grouper (Epinephelus marginatus) in a Mediterranean marine protected area

“…Different colours indicate different individuals, which are listed in ascending order of number of sightings from top to bottom et al 2018). Recent studies reported high spatio-temporal variability in the number of medium-to-large sized fish species occurring at low densities and characterised by patchy distributions, such as groupers (Irigoyen et al 2018;Rojo et al 2021). Variability in abundance estimates can be reduced, theoretically, by increasing the census area and/or by increasing the number of replicates (Underwood 1997;Kulbicki and Sarramégna 1999;Prato et al 2017;Irigoyen et al 2018;Rojo et al 2021).…”

“…Recent studies reported high spatio-temporal variability in the number of medium-to-large sized fish species occurring at low densities and characterised by patchy distributions, such as groupers (Irigoyen et al 2018;Rojo et al 2021). Variability in abundance estimates can be reduced, theoretically, by increasing the census area and/or by increasing the number of replicates (Underwood 1997;Kulbicki and Sarramégna 1999;Prato et al 2017;Irigoyen et al 2018;Rojo et al 2021). In our study, we used widely employed 25 × 5 m 2 strip transects due to i) the limited spatial extension of the area surveyed at each study site (especially Secche Papa) and ii) the need for an acceptable number of replicated counts to estimate variability (i.e., n = 4 per dive and study site).…”

“…In our study, we used widely employed 25 × 5 m 2 strip transects due to i) the limited spatial extension of the area surveyed at each study site (especially Secche Papa) and ii) the need for an acceptable number of replicated counts to estimate variability (i.e., n = 4 per dive and study site). From this perspective, however, new developments in census methods have recently been proposed to maximize the area covered while reducing count variability, including tracked roaming transects, wider and longer strip transects (35 × 20 or 50 × 5 m 2 ), and the use of distance sampling (Prato et al 2017;Irigoyen et al 2018;Rojo et al 2021). As far as individual abundances are concerned, the present study allowed us to photo-identify a total of 94 individuals of dusky grouper at the study sites over the two consecutive summers (2017 and 2018).…”

Quotas regulation is necessary but not sufficient to mitigate the impact of SCUBA diving in a highly visited marine protected area

“…The Cabo de Palos -Islas Hormigas marine reserve (hereafter CPMR) is considered one of the most ecologically effective MPAs in the whole of the Mediterranean Sea (García-Charton et al, 2004;Rojo et al, 2021a;Rojo et al, 2021b), hosting a disproportionally high biomass of the rocky reef fish assemblage compared to other effective Mediterranean MPAs, encompassing high densities of large-size predators around the rocky shoals and small islets characterising the reserve (Rojo et al, 2021a;Rojo et al, 2021b). For this reason, the area is considered one of the most attractive Mediterranean diving destinations, and as a result the number of diving charter businesses operating in the area increased from 1 to 9 since the establishment of the MPA, and the number of divers visiting the MPA each year increased from about 8,000 in 1998 to more than 32,000 in 2017.…”

Performance of a baited underwater video system vs. the underwater visual census technique in assessing the structure of fish assemblages in a Mediterranean marine protected area

“…Besides being one of the main components of biodiversity, fish fauna also play an important role in both the ecological processes of marine ecosystems (Guidetti, 2006) and the economic activities of coastal communities, such as fisheries and sea-related tourism (e.g., diving, snorkeling and excursions; Harasti et al, 2015). Therefore, accurate, rapid, and cost-effective fish assemblage monitoring is a pivotal tool for MPA management (Baker et al, 2016), to verify whether and to what extent the MPA conservation objectives have been achieved, thus evaluating the reserve effectiveness, and redefining these objectives in the framework of the adaptive management (Rojo et al, 2021). In fact, an inadequate assessment of the state of fish assemblages can lead to an increase in exploitation quotas, in the case of excessive estimates of their abundance, or to an unnecessary tightening of restrictions on human activities, in the event of underestimation (Ward-Paige et al, 2020).…”