Browsing by Author "Stergiou, Konstantinos I."
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- Effect of landings data disaggregation on ecological indicatorsPublication . Moutopoulos, Dimitrios K.; Libralato, Simone; Solidoro, Cosimo; Erzini, Karim; Stergiou, Konstantinos I.Ecological indicators calculated from landings data have been extensively used to evaluate the effects of fishing on marine ecosystems. However, few studies have tested the possible effects of gear and spatial aggregation of landings data on different ecological indices over a long-term period. To do this, we applied the Marine Trophic Index (MTI) and Fishing in Balance (FiB) index to Greek landings data disaggregated by gear and area for the period between 1928 and 2010. Aggregated data showed an increase in MTI due to expansion of fisheries that was also confirmed in most of the disaggregated analysis conducted by fishing subareas and main gear types. On the other hand, disaggregated landings by gear and area provided additional insights: while aggregated landings showed no decline in MTI, disaggregated landings showed that 63% of cases indicated an increase in MTI while 11% showed a decline. When small pelagics and other species were excluded, these values changed to 42% and 24%, respectively. Thus, disaggregated data permitted the identification of ecologically meaningful critical situations with decreasing MTI, as has been observed in shallow enclosed gulfs in close proximity to large cities and/or for the main fishing grounds exploited for long periods by seiners (purse and beach). Moreover, disaggregating landings data by gear increased the ability of explaining observed trends, avoiding masking (averaging) effects and accounting for differential development and adaptability of different gear.
- Linking size-based trophodynamics and morphological traits in marine fishesPublication . Rios, Maria F.; Venerus, Leonardo A.; Karachle, Paraskevi K.; Reid, William D. K.; Erzini, Karim; Stergiou, Konstantinos I.; Galvan, David E.The rule of thumb in marine trophodynamics indicates that the bigger an organism, the higher its trophic level (TROPH). This generalization leads to the assumption that fishes increase their TROPH with growth. However, a recent review showed that for many species, TROPH does not increase with body size, suggesting that size-independent feeding is not rare in marine fishes. Here, we assessed some morphological traits of marine fishes that could potentially be used as indicators for the ability to vary TROPH with body size. Stable isotope values of nitrogen were used as a proxy TROPH. The specific objectives were as follows: (a) to evaluate the relationship between the oral gape and the trophodynamic trend and (b) to quantify the relevance of 11 external morphological traits in determining the size-based trophodynamics. We used random forest models to identify the morphological traits that would help predict which species would have the potential to increase TROPH with growth and which would have not. The selected traits included the pelvic fin relative position, the dorsal fin shape, total length, and relative mouth size. Our results also showed a marked relationship between the rate of increase in the oral gape and TROPH. The analyses presented here provide the first comprehensive and quantitative review aiming at linking the trophodynamics of marine fishes with external morphological traits.