Overfishing and the disappearance of short-beaked common dolphins from western Greece

Abstract

Once one of the most common cetaceans in the Mediterranean Sea, the short-beaked common dolphin has declined throughout the region since the 1960s and in 2003 this population was classified as Endangered in the International Union for Conservation of Nature (IUCN) Red List. Here, we document the species' precipitous decline in eastern Ionian Sea coastal waters across 13 yr. While 150 animals were present in the study area (1050 km 2) in 1996, only 15 were observed in 2007. A 12 mo assessment of fishing effort and catch, together with circumstantial evidence, suggests that the decline was caused largely by prey depletion resulting from overfishing. We analyzed the impacts of various fishing gear and estimated the degree of resource overlap between common dolphins and local fisheries. The total biomass removed annually by 308 fishing boats in the study area averaged 3571 t, while that consumed by common dolphins was 17 t. Resource overlap between common dolphins and fisheries-expressed as an average Pianka index of 0.5-differed according to fishing gear, being higher for purse seiners (0.7) and beach seiners (0.4) and lower for bottom trawlers (0.1), trammel boats (0.2) and longliners (0.0). Only about 10 active purse seiners (4% of the total active fishing fleet) were responsible for 33% of the biomass removal, and likely had the greatest impact on prey of common dolphins. This study indicates a high risk of local disappearance of common dolphins in the very near future, unless fishery management measures are implemented immediately. Purse seining should be the main management target.

Ecological mapping and data quality assessment for the needs of ecosystem-based marine spatial management: case study Greek Ionian Sea and the adjacent gulfs

“…About 150 common dolphins were present in 1996, but after 10 years of gradual population shrinking, only 15 animals had remained in 2007 (Bearzi et al, 2008). Bearzi et al (2008) carried out a subsequent assessment of fishing effort and catch and suggested that the decline was largely caused by prey depletion due to overfishing, especially by local purse seiners and beach seiners.…”

“…3). Until 2003, this population covered the entire area, north of the line between the south-western part of Lefkada Island and the southern part of Kastos Island; however, after a dramatic decline, the few individuals left seem to have limited their range to the southern part of Lefkada Island (Bearzi et al, 2008). Very recent data indicate that the remaining individuals of this species may still be trying to expand their presence to their previous range (Tethys Research Institute, unpublished data).…”

Impacts of fisheries on the Critically Endangered humpback dolphin Sousa chinensis population in the eastern Taiwan Strait

“…For example, in the eastern Ionian Sea, the rapid decline of short-beaked common dolphins Delphinus delphis has been caused in major part by resource overlap between dolphins and purse-seine fisheries (Bearzi et al 2006(Bearzi et al , 2008. Fisheries on the Taiwanese west coast are unlikely to target dolphin prey species directly, because these species (e.g.…”

Macro- and micro-geographic variation of short-beaked common dolphin’s whistles in the Mediterranean Sea and Atlantic Ocean

“…The species has to cope with a number of threats arising from human-induced impacts (FORCADA & HAMMOND 1998;TUDELA et al 2005;BEARZI et al 2010) including habitat deterioration, bioaccumulation of pollutants (BORRELL et al 2001;ZHOU et al 2001) and the effects of climate change (BRERETON et al 2010). This situation is more evident in the Mediterranean Sea, where the subpopulation was recently listed as endangered under the 2003 International Union for Conservation of Nature (IUCN) Red List of Threatened Species (BEARZI 2003), as demographic studies demonstrated a strong decline in the population, particularly in the eastern basin (BEARZI et al 2008). The most important remaining habitat for the Mediterranean subpopulation is located in the Alboran Sea, in the western basin (CANÃDAS & HAMMOND 2008).…”