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The 20th Century evolution of Mediterranean exploited demersal resources under increasing fishing disturbance and environmental change
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... Trawling activities on this margin have caused resuspension and erosion of sediments from trawling grounds located along canyon flanks, which have been transported towards deeper areas, significantly increasing sediment accumulation rates within La Fonera, Arenys, Besòs, and Morràs canyon axes during the 1960-70 s (Martín et al., 2008;Puig et al., 2015;Paradis et al., 2017). This resulted from the expansion and industrialization of trawling fleets associated to the growing economic importance of this fishery over that period (Maynou et al., 2006;Sartor et al., 2011;Gorelli et al., 2014). Paradis et al. (2017) suggested that similar enhancements of sedimentation rates could be occurring in other trawled canyons in the Mediterranean margin, or even worldwide, considering the global mechanisation and offshore expansion of trawling grounds to deeper habitats since the mid-XX th century. ...
... Despite the implementation of the 500 HP limit of trawlers set by Spanish law in 1988 (BOE, 1988), real trawler horsepower has been greatly underestimated (Sartor et al., 2011;Gorelli et al., 2014). A relationship between real horsepower and gross tonnage for the Catalan trawling fleet was identified based on real data acquired from interviews to fishermen operating at the neighbouring harbours of Blanes, Palamós, and Tarragona in 2013 , who agreed to provide real engine horsepower values (Fig. 2). ...
... However, after implementing the official 500 HP maximum required for all Mediterranean trawlers when joining the European Union in 1988 (BOE, 1988;Sartor et al., 2011), underreporting of vessel engine power has rendered official data unreliable. Real data of Palamós, Blanes, and Tarragona trawlers in the Catalan margin revealed a continuous increase of total engine power since 1988, resulting from the construction of bigger trawlers and many engine modernizations with horsepower not being adequately declared . ...
Commercial bottom trawling causes some of the largest impacts on the sea floor, and it has been identified as one of the major drivers of sediment resuspension on continental slope regions, particularly in areas surrounding submarine canyons. To assess whether there have been significant trawling-induced alterations in the sediment dynamics within the Foix Canyon (Northwestern Mediterranean) during the past century, sediment accumulation rates obtained using ²¹⁰Pb and ¹³⁷Cs radiochronology were compared between sediment cores retrieved in 1993 and in 2013 from the canyon axis at 860m depth. The results indicate an almost two-fold increase in the sedimentation rate in the 1960-70s, from 0.5cm·y⁻¹ to 0.9cm·y⁻¹, as a consequence of the rapid industrialization of the fishing sector at that time. Sedimentation rates further doubled to 1.8cm·y⁻¹ in the early 2000s. This period was characterized by the construction of bigger trawlers with more powerful engines as well as the modernization of the engines of existing vessels, all of which were largely under-declared. These results provide compelling evidence of the increasing impact of bottom trawling due to the modernization of trawling fleets at the beginning of the XXIst century.
... Fishing effort (FE) was expressed as number of vessels since no time series on fishing days were available. During the fitting process we considered three scenarios for fishing effort: the first didn't consider the increasing technological development the fleets, the second incorporated a technology creep of 0.79 % per year only for trawls (Damalas et al., 2014) and 1 % for the other gears, while the third scenario assumed 0.79 % per year technological creep for trawls and a 2 % increase in the catching efficiency of the 6 remaining fleets based on available literature for the Mediterranean fisheries (Sartor et al., 2011) (Fig. 3). ...
... To address this issue, we assumed annual technology creep factors which lead to more moderate reductions of the nominal fishing effort. Indeed, the best fitting of the model was obtained when maximum technology creep was applied equal to 0.79 % for bottom trawls and 2 % for the remaining gears, as estimated for the Aegean Sea (Damalas et al., 2014) and the Mediterranean Sea (Sartor et al., 2011), respectively. It has been acknowledged worldwide that one of the reasons for the imbalance between resource availability and fishing capacity is technological development (Eigaard et al., 2014). ...
Multiple stressors may combine in unexpected ways to alter the structure of ecological systems, however, our current ability to evaluate their ecological impact is limited due to the lack of information concerning historic trophic interactions and ecosystem dynamics. Saronikos Gulf is a heavily exploited embayment in the E Mediterranean that has undergone significant ecological alterations during the last 20 years including a shift from long-standing eutrophic to oligotrophic conditions in the mid-2000’s. Here we used a historical Ecopath food-web model of Saronikos Gulf (1998-2000) and fitted the time-dynamic module Ecosim to biomass and catch time series for the period 2001-2020. We then projected the model forward in time from 2021 to 2050 under 8 scenarios to simulate ecosystem responses to the individual and combined effect of sea surface temperature increase, primary productivity shifts and fishing effort release. Incorporating trophic interactions, climate warming, fishing and primary production improved model fit, depicting that both fishing and the environment have historically influenced ecosystem dynamics. Retrospective simulations of the model captured historical biomass and catch trends of commercially important stocks and reproduced successfully the marked recovery of marine resources 10 years after re-oligotrophication. In future scenarios increasing temperature had a detrimental impact on most functional groups, increasing and decreasing productivity had a positive and negative effect on all respectively, while fishing reductions principally benefited top predators. Combined stressors produced synergistic or antagonistic effects depending on the direction and magnitude of change of each stressor in isolation while their overall impact seemed to be strongly mediated via food-web interactions. Such holistic approaches advance of our mechanistic understanding of ecosystems enabling us to develop more effective management strategies in the face of a rapidly changing marine environment.
... To take into account the possible improvement in the efficiency of fishing gears due to any form of technological development (known as "technology creep"), a factor of +0.79% per year was assumed for bottom trawls (as estimated by Damalas et al., 2014) and added to the proxy for effort of each year. For the remaining fishing gears for which no information on gear efficiency improvement was available in the study area, alternative levels of the technology creep factor (0%, 1% and 2% per year) were tested based on available literature for the Mediterranean fisheries (Sartor et al., 2011) and elsewhere (Cardinale et al., 2009). The fishing effort for the hindcast period under different levels of technology creep is shown in Figure 2 as relative values (i.e., relative to the value in 1993 used as baseline year). ...
Ecosystem models are important tools for the implementation of Ecosystem Based Fisheries Management (EBFM), especially in highly exploited ecosystems affected by climate change, such as the Mediterranean Sea. Herein, we present the development of an Ecopath ecosystem model for the North Aegean Sea (Eastern Mediterranean) in the early 1990s, as well as the parameterization of the temporal dynamic module (Ecosim) after fitting to catch and relative biomass time series for the period 1993-2020. The Ecosim model included as drivers (i) fishing, assuming a technology creep factor of 2% annual increase (0.79% for bottom trawls), (ii) Sea Surface Temperature, (iii) trophic interactions and (iv) a Primary Production (PP) Anomaly which was positively correlated with the North Atlantic Oscillation of the previous year, highlighting the synergistic effect of environmental and anthropogenic processes during the three-decades hindcast period. Trends in biomasses, catches and ecosystem indicators were characterized by a decline from 1993 to 2010 and a strong recovery thereafter. Sea warming scenarios for the period 2021-2050 indicated contrasting responses to increased temperature among the main commercial groups, while simulations of changes in productivity had relatively straightforward effects. Two scenarios of 10% and 25% reduction in fishing effort revealed quick increases in the biomass of most commercial species, though coupled with lower catches due to reduced fishing, except for few groups that their population increase was remarkably high. Although the 25% effort reduction resulted in high recoveries in the short term, it didn’t necessarily lead to constantly high biomasses resulting in reduced catches towards the end of the forecast period for some groups, in contrast to the 10% reduction. When impacts of reduced productivity were added to temperature effects, the model forecasted lower biomass increases for the winners of sea warming and even higher decreases for the losers. Biomass losses were compensated by a 10% reduction in fishing effort, but this was not overall enough to counterbalance losses in catches. The model developed here contributes to better elucidate observed changes in the past and to hind directions of change in future simulations, as well as to advance EBFM in the area.
... While long time series of data have been collected in the Atlantic Ocean and the North Sea, fisheries time series in the Mediterranean are available only for the last few decades. Current management advice in most cases is based on data starting in the early 1990s (Sartor 2011, Colloca et al. 2013). The availability of 22 years of standardized data obtained from the MEDITS surveys of two of the most important decapods of the demersal communities in the Mediterranean offers a unique opportunity to evaluate trends in abundance at a large scale. ...
The main characteristics concerning the distribution of two of the most important decapod crustaceans of commercial interest in the Mediterranean Sea, the deep-water rose shrimp, Parapenaeus longirostris, and the Norway lobster, Nephrops norvegicus, are studied in the European Mediterranean waters. The study is based on data collected under the MEDITS trawl surveys from 1994 to 2015 from the Gibraltar Straits to the northeastern Levantine Basin (Cyprus waters). The observed differences can be interpreted as different responses to environmental drivers related to the differing life history traits of the two species. In fact, N. norvegicus is a long-living, benthic burrowing species with low growth and mortality rates, while P. longirostris is an epibenthic, short-living species characterized by higher rates of growth and mortality.
... Temperatura superficiale del mare (SST), salinità, intensità di corrente, profondità e sforzo di pesca non hanno mostrato alcun effetto significativo su questa categoria faunistica. L'andamento dell'indice di biomassa al variare del gradiente lati-longitudinale rispecchia quanto riportato in letteratura da numerosi autori (Baino et al. 2007;Ligas et al. 2010a;Pinto 2010) Maynou et al. 2011;Sartor 2011). Gli elasmobranchi sono considerati top predators all'interno della rete trofica, quindi il loro eventuale sovrasfruttamento potrebbe avere un effetto dannoso sull'intero ecosistema alterando il complesso equilibrio che questi predatori provvedono a mantenere (Vacchi et al. 2000;Ligas et al. 2013). ...
Con il declino delle risorse alieutiche provenienti da acque costiere poco profonde, la
crescente domanda e le nuove tecnologie, la pesca si sta espandendo, a livello
globale, in acque sempre più profonde. Nel Mediterraneo tale espansione è motivata
dall'alto valore commerciale dei gamberi di profondità Aristeus antennatus e
Aristaeomorpha foliacea. Un eccessivo sforzo di pesca può comportare un pericolo per
le specie appartenenti alle comunità batiali poiché, a causa dell’elevata longevità,
crescita lenta, maturità tardiva e bassa fecondità, esse risultano più vulnerabili. Inoltre,
anche i fattori ambientali rivestono un ruolo fondamentale nel modellare tali comunità.
Il presente studio è stato rivolto a indagare i possibili effetti della pesca e di alcuni
fattori ambientali sulle comunità dei fondi batiali del Mar Ligure e Alto-Medio Tirreno
tramite analisi delle tre categorie faunistiche di maggior rilevanza (Crostacei, Condroitti
e Osteitti) ivi presenti. Particolare attenzione è stata prestata alla ricerca delle possibili
cause che determinano la segregazione tra Mar Ligure e Mar Tirreno, in termini di
specie prevalente, nella distribuzione di A. foliacea e A. antennatus. I dati provenienti
dalle campagne di pesca a strascico MEDITS (1994-2015), sono stati analizzati,
attraverso modelli Additivi Generalizzati (GAM), al fine di stabilire una relazione tra
biomassa ittica e fattori esterni. I risultati mostrano che la biomassa di Crostacei,
Condroitti e Osteitti è significativamente correlata sia con fattori ambientali, che
antropogenici. Anche la divisione geografica tra i due gamberi A. foliacea e A.
antennatus sembra legata sia a fattori ambientali, che all'effetto della pesca. In
particolare, A. antennatus è prevalente dove lo sforzo di pesca è maggiore (Mar
Ligure). Questo è dovuto alla maggior resilienza di A. antennatus all'impatto della
pesca.
... Indeed, the evolution of the bottom trawling fleets of the ports of Barcelona and Arenys are not only in accordance with those of the port of Palamós 30 , but also with all bottom trawler fisheries operating in the Mediterranean Sea, which have shifted their target species to deep-water crustaceans over this same period 51 .The most relevant bottom trawling European fisheries in the Mediterranean Sea (Italy, Spain, and Greece) augmented substantially between the 1960 s and 1980 s ( Supplementary Fig. S4). This modernization is especially evident for the Italian trawling fleet, which experienced an order of magnitude increase of its fishing fleet and total horsepower, while Spain and Greece tripled the number of operating vessels and total horsepower during this period. ...
Many studies highlight that fish trawling activities cause seafloor erosion, but the assessment of the remobilization of surface sediments and its relocation is still not well documented. These impacts were examined along the flanks and axes of three headless submarine canyons incised on the Barcelona continental margin, where trawling fleets have been operating for decades. Trawled grounds along canyon flanks presented eroded and highly reworked surface sediments resulting from the passage of heavy trawling gear. Sedimentation rates on the upper canyon axes tripled and quadrupled its natural (i.e. pre-industrialization) values after a substantial increase in total horsepower of the operating trawling fleets between 1960 s and 1970 s. These impacts affected the upper canyon reaches next to fishing grounds, where sediment resuspended by trawling can be transported towards the canyon axes. This study highlights that bottom trawling has the capacity to alter natural sedimentary environments by promoting sediment-starved canyon flanks, and by enhancing sedimentation rates along the contiguous axes, independently of canyons’ morphology. Considering the global mechanisation and offshore expansion of bottom trawling fisheries since the mid-20th century, these sedimentary alterations may occur in many trawled canyons worldwide, with further ecological impacts on the trophic status of these non-resilient benthic communities.
Riassunto / Summary
Scyliorhinus canicula (Linnaeus, 1758), Small spotted catfish secondo la FAO, ma noto anche come (aka) Lesser spotted catfish / Lesser spotted dogfish, di seguito cagnolicchio (il nome comune utilizato dai pescatori da Mazara del Vallo in Sicilia) è uno squalo di piccole-medie dimensioni (50-70cm di lunghezza totale, L, in base alla località). Si riscontra sui fondali dell’Atlantico centro-orientale e del Mediterraneo, dalla prossimità delle coste sino a 500-800m (sempre in base alla località). Il cagnolicchio è anche molto comune nelle catture della pesca sia commerciale sia artigianale realizzate principalmente con le reti a strascico e, in misura minore, con attrezzi fissi quali tremagli, palangari e trappole. Nonostante la sua buona consistenza nelle catture in mare, solo gli esemplari più grandi vengono trattenuti per lo sbarco e la vendita nei mercati ittici, ma solo in alcuni porti; in altre marinerie, buona parte (Mediterraneo) o la quasi totalità (Atlantico) deli esemplari viene, infatti, rigettata in mare (aka scarto). In pratica, la maggior parte dei pescatori considera questo piccolo squalo un fastidio per la loro attività. Di conseguenza, dato il risultante basso valore economico della scarsa cattura sbarcata, a questa specie viene solitamente dedicata poca attenzione per la valutazione e gestione da parte delle agenzie ufficiali e dei governi preposti a gestire la pesca marittima. Al contrario, negli ultimi decenni, il cagnolicchio ha attirato l'attenzione sia dei biologi marini che di quelli della pesca (alieutici) a causa dell’inaspettata resilienza mostrata da molti (non tutti!) stock nonostante l'elevato sforzo di pesca e il generale sovra sfruttamento degli altri stock demersali (in particolare di altri squali demersali ad eccezione della specie “gemella” Galeus melastomus). C’è un consenso generale sul fatto che la spiegazione principale di tale elevata resilienza sia la sua elevata capacità di sopravvivere dopo essere fuggito dalle reti in fondo al mare e dopo essere stato rigettato in mare. In sintesi, i cagnolicchi mostrano una notevole “robustezza” e capacità di sostenere e recuperare rapidamente i fattori di stress correlati alle diverse fasi di pesca. Per la rete a strascico, le fasi possono essere riassunte come segue: a) tentativi di evitare il contatto/l'ingresso nell'attrezzo, b) danni subiti nel cercare di sfuffire dall'attrezzo durante la cala (in particolare, attraverso le maglie del sacco), c) non riuscendo a sfuggire, permanenza all'interno del sacco per diverse ore, d) gli shock termici e di pressione sofferti durante il recupero degli attrezzi, e) gli shock termici / visivi / di manipolazione durante lo smistamento a bordo da parte dei pescatori, e f) lo stress subito nel tentativo di tornare sul fondo dalla superficie con l'incertezza di ritrovare i fondali idonei a causa dello spostamento del peschereccio durante la cala (anche di diverse miglia nautiche visto che la velocità di cala si aggira sui 2.5 nodi). Un'altra spiegazione della resilienza è data dall’attitudine dei cagnolicchi a utilizzare come cibo l'elevata quantità di rigetti delle altre specie che raggiungono, moribondi o morti, il fondale. Gli argomenti precedenti sono plausibili, ma non facilmente dimostrabili statisticamente per diversi motivi, principalmente per la difficoltà di ottenere dati rappresentativi, eseguire analisi affidabili (spesso laboriose e costose) e comprendere, nel suo insieme, un ciclo di vita condiviso dalla maggior parte degli studiosi. Alcuni esempi di queste difficoltà sono: 1) una certa confusione nella terminologia e nelle definizioni dei parametri; 2) la discrepanza tra stock in mare e catture/sbarchi poiché quasi tutte le informazioni provengono dalla rete a strascico (quindi la parte dei cagnolicchi che vivono su aree accidentate non sono adeguatamente campionate, 3) l'elevata plasticità mostrata dai diversi stock a seconda della posizione geografica (di solito spiegata con un gradiente Sud N in tutto l'areale, ma non con un gradiente W E nel Mediterraneo), 4) gli alti costi in termini di denaro, personale e requisiti logistici degli esperimenti a bordo o in cattività (in acquario, dove la specie si adatta bene) per stimare la mortalità da pesca collaterale a breve e medio termine dopo la cattura, e 5) la mancanza di un accordo generale tra gli studiosi su molte delle caratteristiche generali dello stock e dei tratti del ciclo di vita (LHT). Per inciso, l'alta plasticità potrebbe spiegare perché i LHT appaiono caotici, contraddittori e bizzarri anche in luoghi contigui. Tra gli LHT, le principali difficoltà riguardano i) il numero e la consistenza della popolazione e dello stock, ii) la distribuzione dei cagnolicchi per profondità e la struttura per taglia / sesso / maturità sessuale, iii) i modelli di crescita / mortalità / accoppiamento / deposizione delle capsule ovigere (EC), iv) la presenza di aree discrete di reclute (nursery) e di riproduzione (spawning) vs aree di riproduzione e reclutamento generalizzate nello spazio, vi) il comportamento alimentare, vii) l'incidenza dei fattori di dipendenza dalla densità e viii) le capacità di produzione/produttività. Scopo del presente documento è quello di tentare una revisione di sintesi del quadro conoscitivo riguardante i cagnolicchi suggerendo, allo stesso tempo, le chiavi interpretative più plausibili (ovviamente, sulla base del sentire dell'autore del presente documento). Allo scopo, innumerevoli pubblicazioni all'interno della letteratura scientifica cd impattata e cd grigia (cioè rapporti tecnici e interni etc.), direttamente o indirettamente correlate ai cagnolicchi, sono state sfogliate, analizzate ed un’ampia selezione inclusa nella Bibliografia. Gli argomenti esplorati spaziano dal fisiologico all'approccio ecosistemico alla pesca. In particolare, per quest'ultimo settore, come precedentemente evidenziato, nonostante l'enorme mole di dati raccolti e analisi effettuate, il grado di condivisione sui LHT dei cagnolicchi e del loro grado di resilienza allo sfruttamento della pesca sembra rimanere basso. Inoltre, i cagnolicchi sfruttati nel Mediterraneo sono raramente (indagini sperimentali) e quasi mai (indagini commerciali) inclusi tra le specie bersaglio/principali (cioè quelle “main species” su cui si dovrebbero produrre regolarmente i piani ufficiali annuali di valutazione e gestione). Come il presente documento cercherà di evidenziare, la letteratura indica chiaramente come ci siano alcuni elementi su cui esiste uno scarso consenso generale tra gli studiosi. Alcuni esempi di controversie riguardano I) la scelta tra pochi stock geografici diffusi invece di molti piccoli stock sparsi e II) se le differenze nella taglia massima individuale riflettano un gradiente latitudinale o uno pseudo nanismo degli stock Mediterranei rispetto a quelli Atlantici (ma uno pseudo nanismo è stato proposto anche tra i cagnolicchi del Centro Nord e C Sud Atlantico e quelli del Mediterraneo E e W). Altri aspetti poco chiari riguardano l'incertezza nelle stime, i conflitti nelle interpretazioni, le frasi contrastanti e la circolarità nelle argomentazioni. L'elemento più critico negli studi sui cagnolicchi è rappresentato dalla cosiddetta "sindrome del compartimento singolo", cioè ogni parametro è generalmente discusso con poca considerazione critica sulla corrispondenza e congruità con le stime degli altri parametri disponibili. Ad esempio, le femmine dei cagnolicchi sono quasi universalmente considerate avere una taglia massima inferiore a quella dei maschi raggiungendo però dopo la maturità sessuale; di conseguenza, ci si dovrebbe aspettare che le femmine subiscano una mortalità (naturale, M, o totale, Z) più elevata dei maschi. Tuttavia, ad un esame più approfondito, il rapporto tra i sessi, la maggior parte delle lunghezze massime e le mortalità appaiono in genere equilibrate e comparabili fra i due sessi. L'Autore del presente documento spera che le 19 schede con delle domande e risposte sui cagnolicchi (organizzate in Tesi, Antitesi e - più plausibile - Sintesi, con una premessa introduttiva) possano aiutare tutti i lettori interessati coinvolti nei diversi campi delle scienze marine, per elaborare un piano di ricerca comune/multidisciplinare per individuare in Scyliorhinus canicula (il cagnolicchio dei pescatori di Mazara del Vallo) un buon candidato per costruire un modello ecosistemico dove le interazioni tra ciclo di vita e resilienza all'intensità della pesca possano essere quantitativamente legate all'ambiente generale / ecosistema in cui vivono questi pesci. Il punto di partenza però dovrebbe consistere nello svolgere delle valutazioni il più possibile complete e integrate a partire da stock unitari identificati su piccola scala (local population), almeno in una prima fase coincidenti con le singole Sub aree geografiche. Inoltre, i ricercatori nelle interpretazioni dei risultati non dovrebbero farsi condizionare da ciò che accade nelle altre sub aree data la plasticità di questa specie che sembra adattare il proprio ciclo vitale (in modo quasi incredibile) alle specifiche caratteristiche geo-morfologiche, oceanografiche e biotiche (non escludendo l’attività di pesca) delle diverse località da cui, almeno in parte, deriva la sconfortante sensazione di enorme e contradittoria variabilità anche confrontando sub aree contigue.
Parole chiave – Pesci cartilaginei, Scyliorhinus canicula, Gattuccio, Cagnolicchio, Revisione della letteratura scientifica, Approccio ecosistemico alla pesca, Oceano Atlantico Orientale, Mare Mediterraneo.
Summary
Scyliorhinus canicula (Linnaeus, 1758), Small spotted catfish according to FAO, but aka Lesser spotted catfish / Lesser spotted dogfish, herein “cagnolicchio” (the vernacular / common name employed by fishers from Mazara del Vallo), represents a small / medium sized shark (up 50-70cm of Total Length depending on the location) usually occurring on the bottom of the Eastern North and Central Atlantic and Mediterranean Sea from nearshore down to around the lower edge of the epibathyal (500m) and mesobathyial depth horizon (ca 800m), depending on the location. The cagnolicchio is also a very common occurrence within the gross catch of both commercial and small scale (artisanal) fisheries, mainly caught by bottom trawl, and in a less extent, by set gears such as trammel nets, longlines and traps. However, notwithstanding its medium - high consistency in the gross catch, only the large sized specimens of cagnolicchio might be observed in landings and sold at fish markets, but only in some fishing harbours. As a matter of fact, fishers usually return to the sea (aka discard) almost all (Atlantic) and the most part (Mediterranean) of the cagnolicchi caught in their gears even considering this small shark a nuisance for their activity. Consequently, little attention is usually devoted in the assessment and management of cagnolicchi by the official fisheries bodies and governments since its low economic value resulting from the combination of low landings and low unit prize. On the contrary, in the last decades, the cagnolicchio has attracted the attention of both marine and fisheries biologists for the ascertainment of an unexpected resilience of many (not all!) stocks to fisheries in spite of the high fishing effort and general over exploitation of the other demersal stocks (especially other demersal sharks with the exception of the twin species Galeus melastomus). There is a general consensus that the main explanation of such as high resilience should be its high capability to survive after escaping from the gears and after being returned to the sea and, as a corollary, its capability to support and quick recover the stressors correlated to the different fishing phases. For the bottom trawl, the phases can be summarised as follows: a) attempts to avoid contacting / entering the gear, b) damages suffered escaping from the gear during the haul (especially through the cod end mesh), c) permanence within the cod end for one up several hours, d) the thermal / pressure shocks during the gear retrieval, e) the thermal / visive / handling shocks during the sorting on board by fishers, and f) the stress suffered trying to return to the bottom from surface with the uncertain of finding suitable grounds since the spatial displacement of the fishing boat during the catch process (bottom trawl) and sorting. A secondary, although related fact supporting the resilience of cagnolicchi, consists in their likely attitude to feed to the high quantity of discards which reach the bottom after being dyed on the deck of vessels or immediately after discard. The previous arguments are plausible, but not easily statistically demonstrable for different reasons, mainly for the difficulty in getting representative data, performing reliable analyses (often laborious and expensive), and figuring out a complete life cycle shared by the most part of scientists. Some examples of sources of difficulties are: 1) some confusion in terminology and parameter’s definitions; 2) the discrepancy between standing stock at sea and landings (since almost all information came from bottom trawlers, hence the part of the cagnolicchi living on rough grounds are not appropriately sampled and most of the caught specimens discarded), 3) the high plasticity showed by the different stocks according the geographical location (usually explained with a South N gradient in the whole areale, but not a W E gradient in the Mediterranean Sea), 4) the high costs in terms of money, staff and logistic requirements of the on board / in aquarium (where the species fits very well) experiments to estimate short- and medium- post catch collateral fishing mortality, and 5) the lack of general agreement among scientists about many of the general stock features and life history traits / stages (LHT) of the cagnolicchi By the way, the high plasticity explains why the LHT might appear chaotic or bizarre even in contiguous locations. Among the LHT, the main difficulties concern i) the number and consistency of population and stock, ii) the depth distribution by size / sex / sexual maturity, iii) the growth / mortality / mating / spawning patterns, iv) the occurrence of discrete nurseries / spawning areas vs generalized (diffuse) spawning and hatching areas, vi) the feeding behaviour, vii) the incidence of density dependence factors, and viii) the production / productivity capabilities. Aim of the present document was to attempt a revision of the cognitive framework concerning the cagnolicchi suggesting, at the same time, the most plausible explanations (obviously, based on the author's feelings of the present document). To do this job, countless publications within both the official (i.e., ISI Journals) and grey (i.e., technical and internal reports etc.) scientific literature (directly or indirectly related to cagnolicchi) were browsed, analysed, and a selection included in the Bibliography. The scientific fields explored span from biomedical / physiological up ecosystem approach to fisheries. In particular, for the latter field, as previously evidenced, in spite of the huge amount of data collected and analysis performed, the degree of knowledge about the cagnolicchi LHT and responsiveness to fisheries exploitation seems to remain quite low. Further, the cagnolicchi exploited in the Mediterranean Sea are rarely (experimental surveys) and almost never (commercial surveys) included among the target (experimental) / main (commercial) species (i.e. those species about which year based official assessment and management plans should be carried out regularly). As the present document will highlight, the literature clearly indicate how there are some items about which there is a weak general consensus among scientists. Some examples of such as controversies regard the choice between few widespread geographical instead of many small scattered stocks (even as stock let) and the maximum individual size reached usually related to a latitudinal gradient or a pseudo nanism of Mediterranean stocks compared with Atlantic counterparts (but nanism / dwarfism, was proposed also between Central North and C South Atlantic and Eastern and Western Mediterranean). Other grey sides showed by the pertinent literature concern the uncertainty in the estimations, conflicts in the interpretations, contrasting sentences, and circularity in the argumentations. The most critical item in cagnolicchi studies may be represented by the so called “single compartment syndrome”, i.e. each parameter is generally discussed with little critical consideration about the match-mismatch with the definitions of the other parameters available. For example, females cagnolicchi are almost universally considered reaching a smaller maximum size (also maturing later) than males. Consequently, females should be expected to suffer a higher natural (M) or total (Z) mortality. However, the current sex ratio and most of the maximum lengths / mortality estimates look quite balanced / comparable. The Author of the present document hopes that the 19 questions about cagnolicchi (organized in Thesis-, Anti-Thesis and - most plausible – Synthesis, with an introductive premise) might help all the interested readers, involved in different fields of marine science, to elaborate a common / multidisciplinary research plan to individuate in Scyliorhinus canicula (the cagnolicchio of fishers from Mazara del Vallo) a nice candidate to build up an ecosystem fishery based model where the interactions between life cycle / resilience to fishing intensity might be quantitatively linked to the ecosystem where the cagnolicchi live. The starting point, however, should be to carry out assessments that are as complete and integrated as possible from unit stocks identified on a small scale (local population), at least in a first phase coinciding with the individual Sub areas. Moreover, researchers should not be influenced, in the interpretations of the results, by what happens in the other sub-areas given the plasticity of this species that adapts its life cycle in an almost incredible way to the specific geo-morphological, oceanographic and biotic characteristics (not excluding fishing activity) of the different locations from which, at least in part, derives the discouraging feeling of enormous and contradictory variability even comparing contiguous sub-areas.
Key words – Cartilaginous fish, Scyliorhinus canicula, Small spotted dogfish, Catfish, Cagnolicchio, Literature review, Ecosystem approach to fisheries, Eastern Atlantic Ocean, Mediterranean Sea.
Sin dal 1985, le campagne di ricerca sperimentali con rete a strascico nei mari italiani hanno costituito un asse portante nel monitoraggio della condizione degli stock demersali sfruttati dalla pesca commerciale. In particolare, le campagne svolte nell’ambito di due progetti principali (GRUND e MEDITS) hanno permesso la costituzione di una importante banca dati utilizzata per produrre una moltitudine di studi e di valutazioni dei parametri biologici e capacità produttiva degli stock. In questo documento, si ricostruisce sinteticamente la genesi e i vari sviluppi di queste attività di raccolta dati che, va sottolineato, restituiscono delle istantanee degli stock in mare in modo diretto e indipendente dall’evoluzione delle strutture e attività delle flotte commerciali. Infatti, le campagne sperimentali sono caratterizzate dall’essere attuate sotto il controllo dei ricercatori. Di contro, le campagne indirette utilizzate per monitorare le flotte commerciali campionano attività al di fuori del loro controllo diretto. La sub area di campionamento nota come Sud Sicilia (sub area geografica SAG 16) è stata utilizzata spesso come esempio per le problematiche che i ricercatori (e non solo loro) debbono affrontare e risolvere nella progettazione ed esecuzione delle campagne sperimentali con rete a strascico. Infine, alcuni molluschi cefalopodi sono stati utilizzati come esempi di come vengono trattate le diverse specie oggetto di studio.
Submarine canyons are preferential pathways for transport of particulate matter and contaminants from the shelf to the deep sea. The Gulf of Palermo continental margin has a very narrow shelf (about 2–3 km wide on average) and is incised by several submarine canyons that favour shelf-slope sediment transfer. A sediment core collected on the outer shelf and six sediment cores taken at different depths along the Oreto, Eleuterio and Anerella submarine canyons were analysed to study the transfer and historical record of trace metal contamination in the Gulf of Palermo continental margin. Trace metals, major elements, organic carbon and sediment grain size were analysed in these cores, which were dated with ²¹⁰Pb to assess their historical compositional evolution since the late 19th century. Hg, Pb, Cu, Zn and Cd content increased until the 1970s and 1980s, associated with the increase in urbanization and industrial activities in the Palermo area, and Hg was the contaminant that reached the highest enrichments. However, the increasing trend of these metals contamination was reversed in the 1970s and 1980s, coinciding with drastic changes in the terrigenous content and grain size of sediments in the canyon axes. These changes occurred when bottom trawling fleets expanded to deeper fishing grounds equipped with powerful trawlers around the Gulf of Palermo canyon heads and flanks and along the Oreto canyon axis. Bottom trawlers have resuspended large amounts of sediment, which have been transferred into the canyons since the 1970s and 1980s and have thus increased sediment accumulation rates. This resuspended sediment has been mixing with the sediment transferred and accumulated along the canyons, diluting and reducing its trace metal contamination levels since the expansion of the bottom trawling fleets.
Conservation and management of shark populations is increasingly becoming important in many marine regions, since there is a growing body of evidence showing that several species are threatened and continuing to decline because of unregulated fishing. Quantifying the extent of sharks' decline, the risk of species extinction, and the consequences for marine ecosystems have been challenging and controversial, mostly due to data limitations.
In this study, more than one century of multiple‐sources of bibliographic records on presence and frequency of occurrence of three species of commercial sharks, the smooth‐hounds Mustelus spp ., in the Mediterranean Sea were compiled and analysed. Generalized additive models for location, scale and shape (GAMLSS) were used to estimate the rate of change of two of these species, Mustelus mustelus and Mustelus punctulatus , in four Mediterranean regions.
Model results showed that smooth‐hounds have declined by 80–90% since the beginning of last century to almost disappear in a large part of their original distributional range during the 1980s and 1990s.
Based on modelling results, a revision of the current International Union for Conservation of Nature classification of Mediterranean smooth‐hounds would be advisable along with the application of urgent conservation measures.
Link to Item http://hdl.handle.net/1834/8539 |3l-B ull. lnsr. O<*éam›_i_›r. Pêche, Salamnibô. l97I. vol. 2. n" 2 LISTE COMMENTEE DES SELACIENS DE TUNISIE par Jean-Pierre Quignard(1) et Christian Capapé (1) RESUME Les auteurs concluent à la présence certaine. sur les côtes de Tunisie. d`au moins 44 espèces de Sélaciens dont ils précisent également les répar-titions balhymétrique et géographique. ABSTRACT The buthymetric and geographic distribution of 44 species of Selacians from the Tunisian coast are presented.
In the present work we integrate the available quantitative information on the following aspects of the Hellenic Seas: (a) distribution of temperature and salinity, water masses, currents and climate change; (b) distribution of oxygen and nutrients in coastal and open sea waters; (c) plankton abundance, production and assemblages; (d) benthic abundance, diversity and assemblages; (e) fish abundance, diversity, assemblages, biology and population dynamics; and (f) fisheries catch trends and variability, wholesale value of catches, catch-effort relationship and catch species composition for 1964-89. Such an integration may possibly form an ecological basis for the management of the Hellenic and Eastern Mediterranean resources. The available chemical and biological data clearly indicate the highly oligotrophic nature of the Hellenic waters. However, within this oligotrophic environment relatively eutrophic areas do exist. Thus, nutrient concentrations as well as plankton and benthos abundance and/or productivity are all by one order of magnitude higher in the N-NW Aegean Sea than in the Ionian and S-SE Aegean Seas, with the latter area being one of the most oligotrophic areas of the world ocean. Similarly, fish catch densities decline from 2.13 km-2 in the N-NW Aegean Sea, to 0.62 km-2 in the S-SE Aegean Sea. The factors responsible for such a differentiation are also discussed. The available data also show that Hellenic fisheries resources, especially the demersal and inshore ones, are overfished. This is the result of the increased fishing effort, the intense modernization of the Hellenic fleet, and the inadequacy of the technical managerial measures currently in use (e.g. closed seasons, minimum mesh size regulations, minimum landing sizes, effort limitations). The latter is mainly attributed to the multi-gear and multi-species nature of the Hellenic fisheries that poses certain difficulties in designing and implementing uniform protective measures, particularly so for the demersal and inshore fisheries. The managerial measures currently in use should be either replaced or complemented by the creation of marine harvest refugia, which provide a refuge in space rather than a refuge in numbers, the latter being the aim of most traditional fisheries management measures.
The Greek monthly catches of bogue, chub mackerel, hake (together with blue whiting), and Mullidae all exhibited an increasing trend during 1964-1987 whereas those of red pandora exhibited a declining trend and those of sardine did not display any significant trend during the same period. The monthly catches of the pelagic species bogue, sardine and chub mackerel were consistently higher in April-October. This is related to the seasonal offshore and inshore migrations of small pelagic fishes and the nature of the Greek purse-seine fishery. The catches of hake, Mullidae and red pandora (demersal species) were consistently lower in June-September, when trawling is prohibited in Greek waters.
Seasonal precipitation variability in the east of the Iberian Peninsula is weakly linked to the North Atlantic Oscillation (NAO) during autumn and winter. For the purpose of improving the study of its performance, low-frequency variability patterns specific to the Mediterranean basin have been searched for. In this way, the Western Mediterranean Oscillation (WeMO) has been defined by means of the dipole composed, in its positive phase, by the anticyclone over the Azores and the depression over Liguria, and its index (WeMOi), as a result of the difference of the standardised values in surface atmospheric pressure in San Fernando (Spain) and Padua (Italy). This new index allows the detection of the variability relevant to the cyclogenesis next to the western Mediterranean basin, which determines in a predominant way the types of rainfall in the Gulf of Valencia. In this area, the WeMO is significantly better than the NAO to explain the monthly pluviometric anomalies during these seasons. Also, a daily resolution of the WeMOi can provide a useful tool to forecast torrential rainfall events in the north-western zones of the Mediterranean (eastern part of the Iberian Peninsula and the south of France), and such significantly daily rainfall frequencies for different thresholds. Copyright © 2006 Royal Meteorological Society.