Athanassios C. Tsikliras

Editorial note on weight-length relations of fishes

Weight-length relations of fishes are useful for estimation of biomass from length observations, e.g., infisheriesorconservationresearch.Hereweprovidesomeguidancetoauthorsofsuchpapers,inordertofacil- itatethepublicationandreviewprocess.

The Mediterranean and Black Sea Fisheries at Risk from Overexploitation

The status of the Mediterranean and Black Sea fisheries was evaluated for the period 1970-2010 on a subarea basis, using various indicators including the temporal variability of total landings, the number of recorded stocks, the mean trophic level of the catch, the fishing-in-balance index and the catch-based method of stock classification. All indicators confirmed that the fisheries resources of the Mediterranean and Black Sea are at risk from overexploitation. The pattern of exploitation and the state of stocks differed among the western (W), central (C) and eastern (E) Mediterranean subareas and the Black Sea (BS), with the E Mediterranean and BS fisheries being in a worst shape. Indeed, in the E Mediterranean and the BS, total landings, mean trophic level of the catch and fishing-in-balance index were declining, the cumulative percentage of overexploited and collapsed stocks was higher, and the percentage of developing stocks was lower, compared to the W and C Mediterranean. Our results confirm the need for detailed and extensive stock assessments across species that will eventually lead to stocks recovering through conservation and management measures.

Climate-related geographic shift and sudden population increase of a small pelagic fish (Sardinella aurita) in the eastern Mediterranean Sea

Abstract Round sardinella (Sardinella aurita) is a thermophilous small pelagic clupeid fish that is exploited by the purse-seine fishery across the Mediterranean Sea. For many years, its Aegean Sea distribution has been confined to the southern part of the sea because of its preference for warmer waters. Recently, the geographic distribution of round sardinella, as reflected in purse-seine catches, has gradually shifted, expanding towards the north. The northward expansion is directly related to the sea warming observed in the northern Aegean Sea. Besides its distribution extension, the population of round sardinella in the northern Aegean Sea exhibited a 30-fold increase since the early 1990s and showed a positive correlation to sea surface temperature. Distributional changes and population outbursts may have detrimental ecological effects to the community and ecosystem but may also affect the local fisheries economics by altering the composition and amounts of catches.

Farming up Mediterranean Food Webs

One of the effects of fisheries on ecosystems is that they tend to remove the larger, higher-trophic-level species and thus progressively lower the mean trophic level (TL) of the landings. This effect is known as “fishing down the food web” (Pauly et al. 1998; but see also Essington et al. [2006] for addition of low-TL fisheries instead of decline in high-TL fisheries, termed “fishing through marine food webs”). At the same time, however, mariculture efforts, originally devoted mainly to low-TL invertebrates, such as mussels or oysters (see Bardach et al. 1972), are increasingly concentrating on producing high-TL fish (i.e., “farming up food webs”; Pauly et al. 2001). Indeed, the mean-weighted TL of mariculture products in countries such as Chile, Canada, Norway, and the United Kingdom increased since 1970 (Pauly et al. 2001). Here, we used Food and Agriculture Organization (FAO) mariculture (brackish aquaculture was excluded) production data (Aquaculture Production: Quantities 1950–2004 database for mariculture; FishStat Plus, version 2.31) and estimates of the fractional TL of the farmed species as given in FishBase (www.fishbase.org; Froese & Pauly 2007) and Stergiou and Karpouzi (2003) to assess the trophic signature of the Mediterranean marine aquaculture industry. In aquatic ecosystems TL can have values of between 2.0, for herbivores and detrivores, and >4.5, for piscivores and carnivores (see www.fishbase. org for methods for its estimation). In 2004 (the most current statistics available), mariculture production of farmed species in the Mediterranean was dominated by the Mediterranean mussel (Mytilus galloprovincialis) (38%), gilthead seabream (Sparus aurata) (29.5%), seabasses (Dicentrarchus labrax and D. punctatus) (27%), and, to a lesser extent, oysters (Ostrea spp. and Crassostrea spp.) (3.5%). The production of herbivorous species (TL = 2), such as bivalves (mussels and oysters), increased from approximately 2,000 t in 1970 to over 100,000 t in 2004. At the same time, the mariculture of intermediate predators (TL = 3.1–4.0; e.g., S. aurata,

A phenotypic trade-off between previous growth and present fecundity in round sardinella Sardinella aurita

The decision of how to allocate surplus energy to reproduction and growth can have important effects on fish population dynamics as well as on other life history traits. The natural examples on the interrelationship between maternal growth and number of offspring produced in fishes are scarce. We tested the hypothesis that these traits are competing for resources by estimating maternal previous growth decisions, using back-calculation, and present reproduction, expressed as absolute fecundity, of female round sardinella (Sardinella aurita) in the northeastern Mediterranean Sea. Despite the overall increasing trend of fecundity with age, individual fecundity was negatively related to individual specific growth rate between the most recent annulus formation and spawning within ages. A decreasing trend between previous growth rate and present fecundity emerged, showing that round sardinella allocate increasingly less energy to growth with age and more into reproduction and that the previous growth decisions determine present fecundity.

Fish market prices drive overfishing of the 'big ones'.

The relationship between fish market price and body size has not been explored much in fisheries science. Here, the mean market prices and fish body size were collected in order to examine the hypothesis that large fish, both among- and within-species, are being selectively targeted by fisheries because they may yield greater profit. Trophic levels, vulnerability to fishing and global landings were also collected because these variables may also be related to the market fish price. These relationships were examined using generalized additive models (GAM), which showed that, among species, fish market price was positively dependent on maximum total length (P = 0.0024) and negatively on landings (P = 0.0006), whereas it was independent of trophic level (P > 0.05) and vulnerability to fishing (P > 0.05). When the fish price vs. size relationship was tested within-species, large individuals were consistently attaining higher market prices compared to their medium and small-sized counterparts. We conclude that the selective removal of the larger fish, which is driven by their market price and to a lesser extent by their availability, may contribute to their overfishing.

EDITORIAL NOTE ON REPRODUCTIVE BIOLOGY OF FISHES

Fish reproductive biology (onset and duration of spawning, sex ratio, maturity stages, length and age at maturity, and fecundity) is important in fisheries research, stock assessment, and management. In this editorial note, we provide some criteria and recommendations on issues of fish reproductive biology, which may be useful in research planning, data analysis and presentation, as well as in manuscript preparation.

Shift in trophic level of Mediterranean mariculture species.

The mean trophic level of the farmed fish species in the Mediterranean has been increasing. We examined the farming-up hypothesis (i.e., the increase in the production of high-trophic-level species) in the Mediterranean by determining the trophic level of the aquafeeds (i.e., what the fish are fed) of 5 species of farmed marine fishes: common dentex (Dentex dentex), common pandora (Pagellus erythrinus), European seabass (Dicentrarchus labrax), gilthead seabream (Sparus aurata), and red porgy (Pagrus sp.). The mean trophic level of aquafeed used in mariculture from 1950 to 2011 was higher (3.93) than the prey farmed fish consume in the wild (3.72) and increased at a faster rate (0.48/decade) compared with that based on their diets in the wild (0.43/decade). Future expected replacement of the fishmeal and oil in aquafeeds by plant materials may reverse the farming-up trend, although there are a number of concerns regarding operational, nutritional, environmental, and economic issues. The farming-up reversal can be achieved in an ecologically friendly manner by facilitating the mariculture of low-trophic-level fishes and by promoting high efficiency in the use of living marine resources in aquafeeds.

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

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 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 οC to 16.2 οC in the Aegean Sea and from 10.0 οC to 14.7 οC in the Ionian Sea. Overall, the rate of MTC increase was 1.01 οC per decade for the Aegean and 1.17 οC per decade for the Ionian Sea and was positively related to sea surface temperature 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 οC 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 favour of the former and that this change is linked to sea surface temperature increase, both internally (through the Atlantic Multidecadal Oscillation) or externally (warming trend) driven.

Gap analysis on the biology of Mediterranean marine fishes

We estimated the current level of knowledge concerning several biological characteristics of the Mediterranean marine fishes by carrying out a gap analysis based on information extracted from the literature, aiming to identify research trends and future needs in the field of Mediterranean fish biology that can be used in stock assessments, ecosystem modeling and fisheries management. Based on the datasets that emerged from the literature review, there is no information on any biological characteristic for 43% (n = 310) of the Mediterranean fish species, whereas for an additional 15% (n = 109) of them there is information about just one characteristic. The gap between current and desired knowledge (defined here as having information on most biological characteristics for at least half of the Mediterranean marine fishes) is smaller in length-weight relationships, which have been studied for 43% of the species, followed by spawning (39%), diet (29%), growth (25%), maturity (24%), lifespan (19%) and fecundity (17%). The gap is larger in natural mortality for which information is very scarce (8%). European hake (Merluccius merluccius), red mullet (Mullus barbatus), annular seabream (Diplodus annularis), common pandora (Pagellus erythrinus), European anchovy (Engraulis encrasicolus), European pilchard (Sardina pilchardus) and bogue (Boops boops) were the most studied species, while sharks and rays were among the least studied ones. Only 25 species were fully studied, i.e. there was available information on all their biological characteristics. The knowledge gaps per characteristic varied among the western, central and eastern Mediterranean subregions. The number of available records per species was positively related to total landings, while no relationship emerged with its maximum reported length, trophic level and commercial value. Future research priorities that should be focused on less studied species (e.g. sharks and rays) and mortality/fecundity instead of length-weight relationships, as well as the economy of scientific sampling (using the entire catch to acquire data on as many biological characteristics as possible) are discussed.