Benthic otter trawl catch data, Porcupine Abyssal Plain, Northeast Atlantic Ocean, RRS Challenger cruise 135, 1997

Study Extent

These data represent the results of processing otter trawl catches (OTSB14; Merrett & Marshall, 1980) from the National Oceanography Centre (NOC, UK) long-term study of the Porcupine Abyssal Plain, including the PAP-Sustained Observatory time-series.

Sampling

These data represent the results of processing otter trawl catches (OTSB14; Merrett & Marshall, 1980) from the National Oceanography Centre (NOC, UK) long-term study of the Porcupine Abyssal Plain, including the PAP-Sustained Observatory time-series. Users should note that we have defined the extent of the PAP-SO as 49° 25´ N 017° 08´ W, 48° 35´ N 015° 52´ W (http://marineregions.org/mrgid/63025), and additionally include data from the wider Porcupine Abyssal Plain (http://marineregions.org/mrgid/4193), this distinction is consistent with that previously applied in the analysis of these data by Billett et al. (2010). These data are presented in quantitative fashion; however, users should note that, in common with other remotely towed samplers, they are likely to represent a substantial underestimation of the true numerical and biomass density of the benthos. Benoist et al. (2019) estimate a general factor of 20 underestimation of biomass density by trawl catch relative to photographic surveys, that estimation appears appropriate for PAP-SO. Similarly, Bett et al. (2001) and Morris et al. (2014) indicate a factor of 20-100 underestimation of numerical density by trawl catch relative to photographic surveys at the PAP-SO. In relation to the various individual body mass and other morphometric measurements presented in this data series, users should note a number of key points: (i) Fresh wet weight and preserved wet weight are variously reported, a 40% loss of body mass may occur during the preservation of larger soft-bodied invertebrates (see, e.g., Billett et al., 2010). Similarly, morphometric measurements are variously reported from fresh and preserved specimens, with the latter potentially subject to shrinkage. Data from fresh and preserved specimens can be distinguished by reference to the fields measurementType and measurementTypeID. (ii) Trawl sampling inevitably results in damage to many specimens, where available, specimen status is reported in the measurementRemarks field. The descriptors used have the following meanings: Intact, the specimen is physically intact, there is no sign of bursting or puncturing, and all major limbs/appendages are present; Damaged, part of the specimen is missing, i.e., it is not physically intact; Dissected, part of the specimen has been dissected for separate analyses; Complete, all parts of the specimen are present, though not necessarily in one piece; Partial, part of the specimen is missing. Users should also note use of the specimen descriptor batch, this refers to counts and/or weights of multiple specimens (or parts thereof). (iii) The various morphometric measurements included are frequently taxon-specific and may be referenced to different morphological features. Information on the detail of these measurements is given in the measurementMethod field (see also the measurementRemarks field). Re-use of such data (for example in the generation of length-weight relationships; see, e.g., Durden et al., 2016) should have regard for these measurement distinctions and potential variations between fresh and preserved specimens [see (i) above].

Method steps

1. Trawl samples are processed and data generated as described in the following papers: Billett, DSM, Bett, BJ, Rice, AL, Thurston, MH, Galéron, J, Sibuet, M, Wolff, GA, 2001. Long-term change in the megabenthos of the Porcupine Abyssal Plain (NE Atlantic). Progress in Oceanography, 50, 325-348. doi: 10.1016/S0079-6611(01)00060-X Billett, DSM, Bett, BJ, Reid, WKD, Boorman, B, Priede, M, 2010. Long-term change in the abyssal NE Atlantic: The ‘Amperima Event’ revisited. Deep Sea Research II, 57, 1406-1417. doi: 10.1016/j.dsr2.2009.02.001

Westmost: -17.191667 [17 11 30 W] Eastmost: -15.383333 [15 23 00 W] Northmost: 50.650000 [50 39 00 N] Southmost: 48.283333 [48 17 00 N]