Acoustic estimates of sperm whale abundance in the Mediterranean Sea as part of the ACCOBAMS Survey Initiative

Acoustic surveys for sperm whales (Physeter macrocephalus) were conducted in the Mediterranean Sea in summer 2018 as part of the vessel-based component of the ACCOBAMS Survey Initiative (ASI). Equal-spaced zigzag transects provided uniform coverage of key sperm whale habitats and were surveyed using a towed hydrophone array deployed from a research vessel at speeds of 5-8 knots. A total of 14,039 km of tracklines were surveyed in the western basin, Hellenic Trench and Libyan waters, with an acoustic coverage of 10% realised for sperm whales. During these surveys, 254 individual sperm whales were detected on the trackline, with an additional 66 individuals off-track. Sperm whales were only seen ten times on-track, with an additional 16 off-track sightings. Estimates of slant range to echolocating whales were used to derive density estimates through both design- and model-based distance sampling methodologies. An acoustic availability of 0.912 (sd = 0.036) was derived from via published models. When correcting for availability bias, a design-based abundance estimates of 2,673 individuals (95% CI 1,739-4,105; CV = 0.21) was derived for the surveyed blocks, which incorporated most known sperm whale habitat in the Mediterranean Sea. The equivalent model-based estimate was 2,825 whales (2,053-3,888; CV = 0.16). Over 97% of detected whales were in the western basin, with highest densities in the Algerian and Liguro-Provencal Basins between Algeria and Spain/France. In the eastern basin, detections were sparse and concentrated along the Hellenic Trench. A density surface modelling (DSM) exercise identified location and benthic aspect as being the most instructive covariates for predicting whale abundance. Distance sampling results were used in a power analysis to quantify the survey effort required to identify population trends. In the most extreme scenario modelled (10% per annum decline with decennial surveys), the population could have dropped by 90% before the decline was identified with high statistical power. Increasing the regularity of surveys would allow population trends to be detected more expediently. Mediterranean sperm whales are listed as Endangered on the IUCN’s Red List and the need for urgent conservation measures to reduce injury and mortality remains paramount for this unique sub-population

Photo-grammetric measurements of swimming speed and body length of basking sharks observed around the Hebrides, Scotland

This work was funded and conducted by the International Fund for Animal Welfare.Photo-grammetric techniques developed for measuring body length and small scale movement patterns of cetaceans were applied to surface swimming basking sharks off the west coast of Scotland. These methods removed the need for close approaches, reducing the likelihood of disturbing the focal animal. Average swimming speed was calculated from the total path length between shark locations measured at approximately one minute intervals. These average speeds varied from 0.49 to 0.73 ms−1 for tracks of between 30 and 170 minutes' duration. Body length measurements ranged between 2.35 and 6.43 m. For ten sharks where body length and swimming speed were measured there was a significant correlation between body length (L) and swimming speed (V) expressed as V = 0.36L033.Publisher PDFPeer reviewe

Encounter rates of cetaceans in the Mediterranean Sea and contiguous Atlantic area

A series of visual-acoustic surveys were carried out in the Mediterranean Sea between 2003 and 2007 from RV 'Song of the Whale'. Almost 21,000 km of trackline were surveyed between the longitudes of 14 degrees W and 36 degrees E with an emphasis on regions with low survey effort. Survey tracklines were designed to provide even coverage probability with random start points. Ten cetacean species were positively identified (sperm whale, fin whale, Cuvier's beaked whale, false killer whale, long-finned pilot whale, Risso's dolphin, common bottlenose dolphin, rough-toothed dolphin, striped dolphin and short-beaked common dolphin). Several of these species, plus sei whale and harbour porpoise, were also encountered in the Atlantic contiguous area (the entrance waters of the Mediterranean between the Iberian Peninsula and north-west Morocco). These surveys expand and clarify the known distributions of cetaceans within the Mediterranean basin. New species documented from Libyan waters include sperm whale, striped dolphin and rough-toothed dolphin. False killer whales and rough-toothed dolphins were documented for the first time off Cyprus. Live harbour porpoises were seen for the first time on Morocco's Atlantic seaboard. It is suggested that the status of rough-toothed dolphins in the Mediterranean be revised from visitor to regular species. Substantial new information on encounter rates is now available for the planning of a basin-wide systematic survey of cetaceans within the Mediterranean Sea and contiguous Atlantic waters.</p

Photo-grammetric measurements of swimming speed and body length of basking sharks observed around the Hebrides, Scotland

Photo-grammetric techniques developed for measuring body length and small scale movement patterns of cetaceans were applied to surface swimming basking sharks off the west coast of Scotland. These methods removed the need for close approaches, reducing the likelihood of disturbing the focal animal. Average swimming speed was calculated from the total path length between shark locations measured at approximately one minute intervals. These average speeds varied from 0.49 to 0.73 ms−1 for tracks of between 30 and 170 minutes' duration. Body length measurements ranged between 2.35 and 6.43 m. For ten sharks where body length and swimming speed were measured there was a significant correlation between body length (L) and swimming speed (V) expressed as V = 0.36L033

Abundance estimates for sperm whales in the Mediterranean Sea from acoustic line-transect survey

The Mediterranean sub-population of sperm whales is believed to be isolated and is classified as Endangered on the IUCN Red List. Although there is evidence to suggest the population is declining, there is a lack of abundance data. A series of acoustic line-transect surveys were undertaken between 2004 and 2013. In 2004, 3,946 km of acoustic effort was conducted in the southern Western Mediterranean basin, resulting in the detection of 159 sperm whales. While in 2007 and 2013, 10,276km of acoustic effort was conducted in the Eastern Mediterranean basin, resulting in the detection of 24 sperm whales. A pooled detection function gave an effective strip half-width of 9.8km. A correction for availability bias was made for each block based on published simulations using data on sperm whale acoustic behaviour: estimates of g(0) were 0.95–0.96. Estimated abundances were: Southern Western Mediterranean Block 634 animals [374–1,077] (95% log-normal confidence interval); Hellenic Trench Block41 [17–100]; Central Aegean Sea Block 33 [5–203]; Herodotus Rise Block 5 [1–28] and Southern Adriatic Sea Block 2 [0–12]. Estimates for allother blocks were zero. The density of sperm whales in the surveyed Southern Western Mediterranean Block was over 17 times higher than for the surveyed Eastern Mediterranean (2.12 and 0.12 whales per 1,000km² respectively). These results, combined with an acoustic survey of the northern Ionian Sea in 2003 and aerial surveys in the northern Western Mediterranean basin in 2010–11, covered approximately 57% of the likely sperm whale habitat in the Western Mediterranean and 75% in the Eastern Mediterranean. Approximate total estimates of sperm whale abundance in the Western and Eastern Mediterranean basins based on extrapolation to the unsurveyed areas are 1,678 and 164 whales respectively. This gives an estimate for the whole Mediterranean Sea of 1,842 animals

Sperm whale abundance estimates from acoustic surveys of the Ionian Sea and Straits of Sicily in 2003

Acoustic surveys for sperm whales, using line-transect methodology, were carried out in the Ionian Sea and Straits of Silcily, Mediterranean Sea, in 2003. A total of 17 whales were detected along 3846 km of designed survey track in the Ionian Sea, and no whales along 892 km in the Straits of Sicily. This total was insufficient to estimate a detection function, so further data were obtained from quasi-random passages made elsewhere in the western Mediterranean in the same year. The encounters included several tight aggregations with inter-animal spacing less then 1 km, primarily from the western Mediterranean. Including individuals from these aggregations distorted the detection function due to the small sample seizes. No such aggregations were found during formal survey of the two areas of interest, and the aggregations were therefore excluded from detection function estimation. The resultant effective strip half-width was 10.0 km (n=40). On the assumption that g(0)=1, the resulting abundance estimates for the Ionian Sea were 62 (with 95% lognormal confidence limits of [24,165]), and 0 for the Straits of Sicily. The low abundance estimate for the Ionian Sea indicates that careful monitoring of the population is needed in the future. During passages along the Hellenic Trench, that were not part of the designed survey, several sperm whales including two aggregations were detected, suggesting that this may be a higher density area and out to be considered as a separate stratum when designing future surveys.</p