Food Consumption Patterns of the Vulnerable Socotra Cormorant Phalacrocorax Nigrogularis Indicate Minimal Overlap with Fisheries in the Eastern Arabian Gulf
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Food consumption patterns of the Vulnerable Socotra cormorant Phalacrocorax nigrogularis indicate minimal overlap with fisheries in the eastern Arabian Gulf S ABIR B IN M UZAFFAR,ROBERT G UBIANI,SONYA B ENJAMIN,RASHID A L S HIHI A HMAD A L -ROMITHI and F AISAL H UMAID A L K AABI Abstract Historically cormorants have come into direct con- Johnsgard, ; Nelson, ). They have frequently flict with fisheries because of their feeding habits. The Socotra come into conflict with fishing communities because of ap- cormorant Phalacrocorax nigrogularis is a regionally endemic parent competition for fish (Nettleship & Duffy, ; seabird restricted to the Arabian Gulf and coastal Oman, and Liordos et al., ; Östman et al., ). Commercial fish- is categorized as Vulnerable on the IUCN Red List. The spe- eries can experience declines in fish stocks as a result of such cies is perceived as being detrimental to local fisheries and is competition (Barrett et al., ; Suter, ; Glahn & therefore persecuted. We studied the diet and estimated the Brugger, ; Glahn & Stickley, ; Price & Nickum, number of Socotra cormorants breeding on Siniya Island, ; Weseloh et al., ; Östman et al., ). Umm Al Quwain, United Arab Emirates, to determine Cormorants may limit recruitment of declining fish stocks their impact on local fisheries. Regurgitated fish loads were (Barrett et al., ); prey on baits used in lobster traps or collected during the breeding seasons of – and on fishing hooks, thus reducing capture rates (Price & –, and the biomass of fish consumed by the Nickum, ); feed from aquaculture ponds housing a var- Socotra cormorant population was estimated. The diet com- iety of farmed fish (Price & Nickum, ); feed on the prey prised seven species of fish, with sailfin flying fish species of commercial fish (Östman et al., ); and cause Parexocoetus mento and blue-stripe sardine Herklotsichthys significant damage to fishers’ nets while diving in pursuit of quadrimaculatus dominating in – and anchovies fish (Nettleship & Duffy, ). (Encrasicholina spp.) dominating in –.Biomassof Other studies, however, have demonstrated that cormor- fish loads was higher in – compared to –,al- ants have a positive effect on fisheries and ecosystem dy- though mean biomass of fish loads did not differ. Dominant namics (Suter, , a,b; Liordos & Goutner, ). fish species in the cormorant’s diet were either used as baitfish They prey on fish species that are not targeted by humans or were non-target species in the fisheries. The low overlap (e.g. Liordos & Goutner, ), feed on fish of smaller between the diet of the Socotra cormorant and the fish landed size classes (Liordos & Goutner, ; Troynikov et al., by the fisheries suggests that the cormorant’s impact on fish- ), selectively feed on and remove sick fish from farms eries is minimal. Conservation strategies to protect the birds (Nettleship & Duffy, ), and cause density-dependent and their feeding areas could safeguard populations of this regulation of fish, thereby enhancing fish diversity and eco- species from further declines. system functioning (Suter, , a,b). Fishers generally Keywords Arabian Gulf, diet, fish biomass, fish landings, perceive cormorants to be a threat to fisheries (Stickley & fishery interactions, impact, Phalacrocorax nigrogularis, Andrews, ; Liordos et al., ; Nelson, ); for ex- Socotra cormorant ample, Mississippi catfish farmers believed that double- crested cormorants Phalacrocorax auritus were the greatest threat to farmed fish in ponds (Glahn & Brugger, ), and Introduction fishers of the Amvrakikos Gulf, Greece, believed that cor- morants were the primary cause of decline in commercial ormorants (Phalacrocoracidae) are piscivorous birds fish stocks (Liordos et al., ). Although some of their per- Cfound in coastal areas or inland waters (Cramp, ; ceptions are well founded (Leopold et al., ), others are baseless (Dalton et al., ). SABIR BIN MUZAFFAR (Corresponding author), ROBERT GUBIANI,SONYA BENJAMIN, The Socotra cormorant Phalacrocorax nigrogularis is a AHMAD AL-ROMITHI and FAISAL HUMAID AL KAABI Department of Biology, College regionally endemic species found in the Arabian Gulf, the of Science, United Arab Emirates University, Al Ain, United Arab Emirates Gulf of Oman and adjoining regions (Javed & Khan, ; E-mail [email protected] BirdLife International, ). It is categorized as Vulnerable RASHID ALSHIHI Marine Environment Research Department, Ministry of Environment and Water, Umm Al Quwain, United Arab Emirates on the IUCN Red List, based on significant population de- Received February . Revision requested March . clines since the s (BirdLife International, ). The Accepted May . First published online October . cormorants are surface-diving piscivores (Cramp, ), Oryx, 2017, 51(1), 115–123 © 2015 Fauna & Flora International doi:10.1017/S0030605315000666 Downloaded from https://www.cambridge.org/core. IP address: 170.106.35.229, on 26 Sep 2021 at 06:00:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0030605315000666 116 S. B. Muzaffar et al. and anecdotal information suggests that their diet probably influence fish stocks by targeting bait or commercial fish includes sardines Sardinella spp., bigeye Selar crume- species. However, a clear understanding of ecological and nophthalmus and yellowtail scads Atule mate, silversides sociological factors could help to facilitate sustainable coex- Atherinomorus lacunosus, spotted halfbeaks Hemiramphus istence of cormorants (or other seabirds) and humans (Van far and streaked rabbitfishes Siganus javus (Jennings, Eerden et al., ) in the Arabian Gulf. We studied the diet ). Disturbance at the breeding colonies is regarded as of Socotra cormorant chicks to better understand the spe- a major threat to the species, and many colonies have cies’ role in the Arabian Gulf and its impact on the commer- gone extinct as a result of oil exploitation and construction cial fishery of the United Arab Emirates. (Jennings, ). Collection of eggs and chicks occurs in many of the western colonies, including Abu Dhabi (Jennings, ; Wilson, ), and recreational shooting Study area of adults seems to be a common practice (Jennings, ) Within the Arabian Gulf the largest breeding concentrations although this has not been quantified. Egg collection, hunt- of Socotra cormorants occur within the Gulf of Salwa. ing of chicks or adults, and disturbance to the breeding habi- Bahrain’s Hawar Islands complex hosted a population of tat are all prohibited under United Arab Emirates Federal c. , pairs during – (Jennings, ; Fig. ), Law # (). and several Saudi Arabian coastal islands hosted ,– The diet of seabirds varies between adults and chicks, , pairs (Jennings, ). Colonies in the western and chick-provisioning offers insight into fish availability, United Arab Emirates collectively host c. , pairs on distribution patterns and long-term changes in the oceanic – islands in Abu Dhabi (EAD, , a,b), and a single environment (Barrett et al., ; Montevecchi, ). The colony on Siniya Island in Umm Al Quwain (Fig. ) is esti- diet of chicks has therefore been used in many seabird stud- mated to host ,–, pairs (Muzaffar, ). ies to examine feeding and foraging ecology (Schreiber & Although current trends suggest that Siniya Island may Burger, ). Cormorants regurgitate food loads (consist- have a larger breeding population, we still consider the ing of intact or partly digested food) and pellets (containing Hawar Islands to be the largest breeding colony, given the feathers, otoliths or bones) at their nesting sites. Both have variability in the size of the breeding population between been used to determine diet, although pellets provide a years (Pilcher et al., ; Jennings, ; Muzaffar, ). higher degree of accuracy (Zijlstra & Van Eerden, ) This study was part of a greater effort to understand breed- provided libraries of fish otoliths are available. ing, foraging ecology and conservation of the species on Regurgitated food can also be valuable in identifying dietary Siniya Island (Fig. ; see Muzaffar et al., , , for components, and is considered to be a suitable index of details of the site). The colony of Socotra cormorants is re- available diet (Barati, ; Emmrich & Düttmann, ). stricted to the north-central part of the island. The habitat The Arabian Gulf is a shallow, highly saline and relatively consists of mixed desert scrub (Haloxylon–Arthrocnemum warm marine system with rapid turnover; it supports fish macrostachyum complex), loose sandy gravel and plantations communities that are species depauperate compared to of Acacia tortilis, Prosopis juliflora and Prosopis cineraria.The other shallow waters at similar latitudes (Sheppard, ; island is under the jurisdiction of the Umm Al Quwain Grandcourt, ). Artisanal, recreational and commercial Municipality and the Ministry of Environment and Water. fishing are carried out there, targeting mostly reef fish, in- The nearest islands with breeding Socotra cormorants are cluding groupers (Serranidae), seabreams (Sparidae), em- km west, in Abu Dhabi (Jennings, ; Fig. ). perors (Lethrinidae), snappers (Lutjanidae), sweetlips and grunts (Haemulidae), jacks (Carangidae) and parrotfishes (Scaridae; Carpenter et al., ; Grandcourt, ). Methods Species such as Sardinella longiceps are also exploited as baitfish, although the extent of this exploitation is not re- Fish loads were collected during the – and – ported (MOEW, ). In recent years sharks and other breeding seasons. We approached