Citizen science and habitat modelling facilitates conservation planning for crabeater seals in the Weddell Sea

Abstract

Aim Creating a network of marine protected areas in the Southern Ocean requires extensive knowledge on species’ abundances, distributions and population trends especially in the Weddell Sea where year‐round pack ice makes most of the Weddell Sea inaccessible. We combine satellite images and citizen science to model habitat suitability for crabeater seals (Lobodon carcinophaga) throughout the Weddell Sea. Location Weddell Sea, Antarctica. Methods High‐resolution satellite images covering 18,219 km2 of the Weddell Sea during crabeater seal breeding season (October—November) were hosted on the crowd‐sourcing platform Tomnod (DigitalGlobe). Citizen scientists marked “maps” where seals were present/absent and these votes were compared with the votes of an experienced observer. Correction factors were used to correct votes to either a continuous probability of seal presence, or a binary seal presence/absence value. We modelled probability of seal presence using ensemble models of Random Forests (RF), Boosted Regression Trees (BRT) and Support Vector Machines (SVM), and used fitted Maxent models to model seal presence/absence data. Results Model predictive power was low (RF: R2 = 0.076 ± 0.002: BRT: R2 = 0.086 ± 0.0008; SVM: R2 = 0.082 ± 0.003) to average (Maxent: AUC = 0.71 ± 0.004). Distance to the ice edge and bathymetry were the most important variables that influenced crabeater seal distribution. Main conclusions Crabeater seals were more likely to be present over abyssal water, which coincides with typical adult Antarctic krill habitat — crabeater seal preferred prey. Where ice concentrations were more variable, that is more accessible, crabeater seals were also more likely to occur. Results agreed with the known ecology of crabeaters seals and the abundance, distribution and ecology of Antarctic krill. We were able to survey the largest area ever surveyed in the Weddell Sea and provide a model to assist furthering policy around the proposed protected area.

Antarctic pack ice seal observations during spring across the Lazarev Sea

“…This agrees with the single largest crabeater seal survey and habitat modelling for the Weddell Sea during breeding season, which showed crabeater seals are rarely found in the deep Weddell Sea, but around the outer fringes of the pack ice and in the northern Lazarev Sea (Wege et al, 2020). This breeding season distribution is associated with typical Antarctic krill (Euphausia superba) habitat (Wege et al, 2020), as it is during the austral summer (Nachtsheim, Jerosch, Hagen, Plötz, & Bornemann, 2017), krill being the key prey species of crabeater seals (Hückstädt et al, 2012). Previous sightings in any year of a crabeater seal pup accompanied by an adult were between 2 October and 15 December in Eastern Antarctica (Southwell et al, 2003), which brackets the timing of sightings of pups in the present study (25)(26)(27)(28)(29)(30)(31).…”

“…Crabeater seals, including triads (n = 1) as defined by Siniff et al (1979), comprising an adult female (presumably the mother) and its pup with an adult male nearby , female-pup pairs (n = 3), singletons (n = 5) and unsexed groups (n = 4) of 2-3 seals were widely dispersed in the marginal sea ice zone (this study). This agrees with the single largest crabeater seal survey and habitat modelling for the Weddell Sea during breeding season, which showed crabeater seals are rarely found in the deep Weddell Sea, but around the outer fringes of the pack ice and in the northern Lazarev Sea (Wege et al, 2020). This breeding season distribution is associated with typical Antarctic krill (Euphausia superba) habitat (Wege et al, 2020), as it is during the austral summer (Nachtsheim, Jerosch, Hagen, Plötz, & Bornemann, 2017), krill being the key prey species of crabeater seals (Hückstädt et al, 2012).…”

“…Crabeater seals breed in the pack ice zone surrounding Antarctica in the austral spring (Siniff, Stirling, Bengtson, & Reichle, 1979;Southwell, Kerry, Ensor, Woehler, & Rogers, 2003) when pack ice is extensive and ship access is difficult (Shaughnessy, Jones, & Viggers, 2019). Consequently, there have been few studies of crabeater seals during their breeding season (Joiris, 1991;Wege et al, 2020). Crabeater seals, including triads (n = 1) as defined by Siniff et al (1979), comprising an adult female (presumably the mother) and its pup with an adult male nearby , female-pup pairs (n = 3), singletons (n = 5) and unsexed groups (n = 4) of 2-3 seals were widely dispersed in the marginal sea ice zone (this study).…”

“…With the exception of the surveys of the north-western parts of the Weddell Sea by Øritsland (1970Øritsland ( ) in 1964Øritsland ( , Erickson (1984 in 1983 and Joiris (1991) in 1988, no other comparable data exist on abundance and densities for pack ice seals in spring in the larger Weddell Sea region. Recently, satellite census data were used to build potential habitat model distributions exclusively for crabeater seals in the entire Weddell Sea (Wege, Salas, & LaRue, 2020).…”

Accuracy and precision of citizen scientist animal counts from drone imagery

“…Citizen science is a potentially useful tool that involves recruiting volunteers from the public without prior experience to complete clearly outlined tasks [ 19 ]. Citizen science has been used to gather and process large datasets for over a decade [ 20 , 21 ], including for research on abundance and distribution of marine mammals [ 22 – 25 ]. Crowd-sourced science requires an up-front investment of time and labor to create a training system for new volunteers [ 26 , 27 ].…”