Mean temperature of the catch (MTC) in the Greek Seas based on landings and survey data

Abstract

The mean temperature of the catch (MTC), which is the average inferred temperature preference of the exploited species weighted by their annual catch, is an index that has been used for evaluating the effect of sea warming on marine ecosystems. In the present work, we examined the effect of sea surface temperature (SST) on the catch composition of the Greek Seas using the MTC applied on the official catch statistics (landings) for the period 1970-2010 (Aegean and Ionian Seas) and on experimental bottom trawl survey data for 1997-2014 (southern Aegean Sea). The MTC of the landings for the study period increased from 11.8 to 16.2 • C in the Aegean Sea and from 10.0 to 14.7 • C in the Ionian Sea. Overall, the rate of MTC increase was 1.01 • C per decade for the Aegean and 1.17 • C per decade for the Ionian Sea and was positively related to SST anomalies in both areas. For the survey data, the increase of the MTC of the bottom trawl catch in the southern Aegean Sea was lower (0.51 • C per decade) but referred to a shorter time frame and included only demersal species. The change in MTC of official and survey catches indicates that the relative catch proportions of species preferring warmer waters and those preferring colder waters have changed in favor of the former and that this change is linked to SST increase, both internally [through the Atlantic Multidecadal Oscillation(AMO)] or externally (warming trend) driven.

The effect of regional sea surface temperature rise on fisheries along the Portuguese Iberian Atlantic coast

“…The MTC index and the percentage of warmer species both displayed increasing trends for all regions; however, the statistical analyses revealed no significant correlations between MTC and SST, a finding that is contrary to the results of other studies conducted in Mediterranean areas (Tsikliras & Stergiou, ), and by Cheung et al () at the global level. In principle, the increase in MTC is indicative of alterations in the relative catch proportions of species showing a preference for warmer waters (thermophilous) and those preferring colder waters (psychrophilous), in favour of the thermophilous species (Cheung et al, ), but the lack of any significant correlation with SST suggests a possible regional role of other environmental factors, such as AMO (Alheit et al, ; Tsikliras et al, ), westerly and northerly winds, river discharge, or upwelling, that affect marine resource distribution and larvae recruitment (Baptista et al, ; Perry et al, ; Ullah, Leitão, Vânia, & Chicharo, ).…”

“…The MTC theory predicts that the increase in MTC is driven by warming. So, to attribute such a relationship there should be a correlation between MTC and SST, or with another proxy of environmental temperature (Cheung et al, 2013;Tsikliras et al, 2015). AMO is an SST-based index that affects marine communities in the Atlantic and the Mediterranean (Alheit et al, 2014;Tsikliras et al, 2015).…”

“…So, to attribute such a relationship there should be a correlation between MTC and SST, or with another proxy of environmental temperature (Cheung et al, 2013;Tsikliras et al, 2015). AMO is an SST-based index that affects marine communities in the Atlantic and the Mediterranean (Alheit et al, 2014;Tsikliras et al, 2015). Thus, the lack of correlation between MTC and SST could have been driven by an AMO SST oscil- as a source of livelihoods, food security, and income for many fisheries-related families along the Leitão, Baptista, Zeller, and Erzini, (2014).…”

“…The mean temperature of the catch (MTC) is an indicator that has been recently proposed in order to assess the effect of global warming on exploited marine communities (Cheung et al, ). The MTC represents the average inferred temperature preference of the exploited species, weighted by their annual catch, which is a proxy for the temperature preference of the naturally occurring fish community, and has been used recently to evaluate the effect of ocean warming globally in large marine ecosystems (Cheung et al, ), in the eastern Mediterranean (Tsikliras & Stergiou, ), in Italy (Fortibuoni, Aldighieri, Giovanardi, Pranovi, & Zucchetta, ), Greece (Tsikliras, Peristeraki, Tserpes, & Stergiou, ), Turkey (Keskin & Pauly, ), and the Caribbean (Maharaj, Lam, Pauly, & Cheung, ).…”

“…Only significant linear regression models are shown (R, coefficient of correlation; P, P value) Total landings (tonnes) between 1989 and 2009 from the north-western (NW), south-western (SW), and southern (S) coasts of Portugal. Only significant linear regression models are shown (R, coefficient of correlation; P, P value)Tsikliras et al, 2015), westerly and northerly winds, river discharge, or upwelling, that affect marine resource distribution and larvae recruitmentPerry et al, 2005;Ullah, Leitão, Vânia, & Chicharo, 2012).…”