Burrow emergence rhythms of Nephrops norvegicus: UWTV, surveying biases and novel technological scenarios

Abstract

The occupancy assumption “one burrow system, one animal” (Sardà and Aguzzi, 2012) raises a number of generic research questions concerning the true occupation of burrows in many Nephrops stocks. The burrow system acts as the centre of a strong territorial rhythmic behaviour (Rice and Chapman, 1971; Farmer, 1975) leading the adults’ lobsters to evict subordinates from burrows in a dominance hierarchy framework (Sbragaglia et al., 2017); indeed, two wild adult lobsters are rarely found in the same shelter (Cobb and Wang, 1985). Other studies showed evi-dence that no spatial segregation occurs between juveniles and adults (Maynou and Sardà, 1997) achieving the establishment of adult-juvenile complexes (at least 1 adult and 1 juvenile per bur-row), which become separated as juveniles grow (Tuck et al., 1994). Moreover, Nehprops bur-rows systems could also be inhabited by other benthic crustacean species (e.g. Munida sp.) or may remain empty and intact for an unknown period of time after animals’ death (Sardà and Aguzzi, 2012). These factors still create uncertainties about the true numbers of animals occupy-ing burrow systems, representing an important issue when providing a relative or absolute index for determination of Nephrops’ stock status (i.e. Harvest Rate; Sardà and Aguzzi, 2012). [...]