GNGTS 2019 - Atti del 38° Convegno Nazionale

602 GNGTS 2019 S essione 3.2 fraught with quandary. Individual variability could lead to hardships while searching for values representative of the population’s average sensitivity. Fish. Fish react to anthropogenic sound sources displaying different behaviour such as being more active, milling in compact schools, ‘freezing’, and dropping to deeper depths (Popper et al., 2003). A decrease of 40% - 80% in catch rates and reduced abundance have been noticed concomitantly with seismic surveys in species such as: Atlantic cod ( Gadus morhua) , haddock ( Melanogrammus aeglefinus ), herring ( Clupea harengus ), and blue whiting ( Micromesstius poutassou ) (Slotte et al., 2004). Other studies report variable results, from no-catch changes in non-mobile species to reduction of 70% in the catch rates of mobile and valuable fin-fish species such as cod and haddock (Aguilar de Soto et al., 2013). Moreover, the impacts of airgun noise on marine fish include: decreased egg viability, a surge in embryonic mortality, or diminished larval growth if exposed to sound levels of 120 dB re 1 μPa ( Booman et al., 1996). Increases in stress hormones have been observed in fish due to noise (Santulli et al., 1999). On the whole, recorded behavioural adjustments are irregular and are often difficult to deduce and to associate with real impacts due to differences in noise sources and discrepancies in reported noise levels, sampling techniques and other drawbacks in methodology ( Knudsen et al., 1992). Invertebrates. There is relatively little information on the effect of underwater noise on the behaviour of marine invertebrates. Various studies have indicated that offshore seismic survey activity has no effect on catch rates of crustaceans in the surrounding area (Parry and Gason, 2006). Wardle et al. (2001) observed little effect on invertebrate populations inhabiting a reef exposed to pneumatic sources. Moreover, low frequency noise has reportedly been used to successfully deter barnacle larvae from settling on ship hulls (Branscomb and Rittschof, 1984) and there is anecdotal evidence of squid being attracted to intermittent, low frequency noise (Maniwa, 1976). Other studies report other species of squid exposed to airgun noise showing strong startle responses involving ink ejection and rapid swimming (McCauley et al., 2000). A bivalve, Paphia aurea, showed modified levels of hydrocortisone, glucose, and lactate when subjected to seismic noise (Moriyasu et al., 2004). In snow crab species Chionoecetes opilio , bruised ovaries and injuries to the equilibrium receptor system or statocysts were also observed (Morris et al., 2018). Fig. 1 - Seismic surveys and the need to lessen the impact on marine fauna.