Food Consumption Patterns of the Vulnerable Socotra Cormorant Phalacrocorax Nigrogularis Indicate Minimal Overlap with Fisheries in the Eastern Arabian Gulf

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 cormorants 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 nesting cormorants elasmobranchs have also been targeted as part of an unregu- during .–., which elicited regurgitation (normally lated market in the United Arab Emirates (Jabado et al., they would attempt to feed the chicks directly). In the ). Fisheries statistics are reported at the family level, pre- – breeding season sampling was carried out early cluding the estimation of species-specific catch data ( October ), when most chicks (. %) had hatched (MOEW, ). The lack of species-specific catch and but were still small and associated with nests, and late ( trade data is regarded as an impediment to adequate fishery November ), when chicks were .  weeks old and management (Jabado et al., ). many were still associated with nest sites but most were Many fish species are exploited at unsustainable rates in forming creches (Gubiani et al., ). Thus, there was a bet- the Arabian Gulf (Grandcourt, ; EAD, a; Jabado ter representation of the diet of chicks of various sizes dur- et al., ). Populations of the Socotra cormorant could ing –.In– fish loads were collected only on

FIG. 1 Distribution of the Socotra cormorant Phalacrocorax nigrogularis in the Arabian Gulf (BirdLife International, ). AD, Abu Dhabi; DU, Dubai; SH, Sharjah; AJ, Ajman; UAQ, Umm Al Quwain; RAK, Ras Al Khaimah

two dates during the breeding season ( November  using one-way ANOVA to examine inter-year differences and  February ), arbitrarily defined as early and late. in diet. Relative abundance and fish biomass were also com- Our observations suggested that one species dominated fish pared between years. Biomass of early and late fish loads was loads throughout the season, and therefore the small sample compared using one-way ANOVA. size could still be representative. Each fish load was placed in Breeding population data for the Socotra cormorant were a labelled ziplock bag and either analysed on site, away from obtained from our ongoing monitoring activity (Muzaffar the colony (–), or frozen within – hours and pro- et al., , ). The total breeding populations during cessed later in the laboratory (–). Each species was the – and – seasons were estimated based photographed, and representative specimens were retained on the density and area of occupancy of breeding pairs. to confirm their identification later. Area of occupancy was mapped in Google Earth (Google  Loads that contained partly digested fish were not used in Inc., Mountain View, USA) and calculated in m . The dens- the analyses. We analysed a total of  fish loads containing  ity of nesting birds was taken from Muzaffar et al. (). individual fish in – and  fish loads containing  in- Variance was estimated following Anderson et al. (). dividual fish in –.Althoughwerecognizethatthese Hatching success was estimated to be .% for – sample sizes are small and there is potential for bias, we believe (Muzaffar et al., ) and .% for – (S.B. that the collection method made sampling representative al- Muzaffar, unpubl. data). Fledging success (the proportion though it had the potential to miss rare species in the diet. of hatchlings that survived to fledging) was estimated to Each individual fish was identified to the lowest possible be . (Muzaffar et al., ) and .% (S.B. Muzaffar, un- taxonomic level using FAO (), Carpenter et al. () publ. data) for – and –, respectively. and FishBase (Froese & Pauly, ), and their standard Fourteen study plots, each containing – nests, were lengths were measured. The biomass of each species was es- monitored once every  weeks to determine the hatching timated using the equation success and fledging success in – (Muzaffar et al., ). Chicks were considered fledged if they were no longer Biomass = b aSL observed in the nest after  days (see details in Muzaffar where SL = standard length. Values of fitting parameters a et al., ). Juveniles and non-breeding adults were esti- and b were obtained from published references for the spe- mated to comprise  and %, respectively, of the breeding cies or genus in FishBase (Froese & Pauly, ). The total population each year, based on the age structure of other number of fish per load, mean biomass of individual fish species of cormorants (Nelson, ). Variance in the esti- from all fish loads, and mean biomass of fish loads were mates of the total numbers of chicks and fledglings was pooled for a given season and compared between years based on variation in the hatching and fledging success in

 plots containing  nests in – (Muzaffar et al., ) and four plots containing  nests in – (S.B. Muzaffar, unpubl. data). Variance in the juvenile, non- breeding adult and breeding adult populations was estimated by resampling the product of the density of nests in the  plots (Muzaffar et al., ) and the area , times with replacement (Manly, ). The number of meals per chick was estimated to be three per day, based on our observations, and it was assumed that one meal represented one fish load. The biomass consumed by the total population of chicks was estimated based on the mean biomass of fish in fish loads consumed during each breeding season ( days). The biomass consumed by fledged chicks was calculated over the entire year ( days), assuming none of the fledged chicks died before the following year. FIG. 2 Comparison of fish consumption by Socotra cormorants Consumption of fish by juveniles and non-breeding and on Siniya Island (Fig. ) during the – and – breeding adults was estimated based on allometric calcula- breeding seasons. The asterisk indicates significant difference at tions in Nagy () and then extrapolated to the total popu- α = .. lation of those age classes in – and –. Field metabolic rate (FMR) was calculated using the following Results equation: Fish loads contained – fish, with a mean of . in –   FMR = . × mass . (Nagy, )  and . in –; the difference was not significant (Fig. ). Mean biomass of individual fish was significantly The mass of a Socotra cormorant was set at , g, based on higher in – (. g) compared to – (. our measurements of adult individuals (S.B. Muzaffar, un- g; one-way ANOVA, n = ,F=.,P, .). Total − publ. data). Energy density of prey was set at . kJ g , fol- biomass per fish load, however, was not significantly differ- lowing Danckwerts et al. (). All quantities of fish ent between years. consumed were converted to tonnes and extrapolated to Seven species of fish were recorded in the fish loads: sail- the entire population in each year. fin flying fish Parexocoetus mento, blue-stripe sardine Fishing occurs extensively within the waters of the Herklotsichthys quadrimaculatus, anchovies Encrasicholina United Arab Emirates (Fig. ) and some areas are fished spp., pink ear emperor Lethrinus lentjan, pickhandle barra- by more than one emirate. Fisheries statistics for  were cuda Sphyraena jello, congaturi halfbeak Hyporhamphus obtained from the Ministry of Environment and Water limbatus, and bigeye scad Selar crumenophthalmus (Fig. ). (MOEW, ). Fisheries statistics for  were not avail- There was little overlap in the composition of the diet be- able and were estimated based on the mean incremental in- tween the  years. Sailfin flying fish were the most numeric- crease in fish landings during – available from the ally dominant species in – (%), whereas anchovies MOEW. These data provide total fish catches in all seven dominated in – (.%). Estimates of fish biomass emirates (Abu Dhabi, Dubai, Sharjah, Ajman, Umm Al revealed that the blue-stripe sardine was more prevalent as Quwain, Ras Al Khaimah and Fujairah), including total prey in – (.%), followed by the sailfin flying catch, total catch of demersal fish and total catch of pelagic fish (.%). In – the mean biomass of fish loads fish. Based on foraging data for Socotra cormorants increased from . to . g during the chick-rearing period (Muzaffar, ) we determined that individuals breeding (one-way ANOVA, F = .,P, .). The diet was com- on Siniya Island were fishing in the waters of Dubai, posed primarily of sailfin flying fish (.%) in the early part Sharjah, Ajman, Umm Al Quwain and Ras Al Khaimah. of the season, followed by a switch to blue-stripe sardine We therefore pooled the landing data for these five emirates (.%) and pink ear emperor (.%). No such change to compare total biomass consumption by Socotra cormor- was evident in the – season, and anchovies re- ants in relation to fish landings. The accuracy of the data for mained the most consumed species throughout the season fish catches is not indicated on the MOEW website, and (% early in the season and .% later). Biomass of fish thus we have presented them as raw total catch, without per load decreased between early (. g) and later (. g) any standard error. All statistical analyses were conducted in the season (one-way ANOVA, F = .,P, .). in Minitab . (Informer Technologies Inc., Shingle Total consumption of fish was estimated to be , ± Springs, USA). SE  tin– and , ± SE  tin–.

FIG. 3 Comparison of the diet of Socotra cormorants on Siniya Island (Fig. ) during the – and – breeding seasons in terms of (a) number of individuals and (b) biomass of prey species. Chicks consumed c.  ± SE  and , ± SE  t during The total tonnage of fish landed by the commercial fisher- the chick-rearing period in – and –, re- ies from the foraging areas of Socotra cormorants was spectively (Table ). Fledglings consumed , ± SE  , tin and , tin. Most of the catch and , ± SE  tin– and –, respect- was composed of demersal fishes (, tin, ively. Total fish biomass consumed by the Socotra cormor- , tin) and none of the commercial catches in- ant population of Siniya Island was , ± SE  and cluded any of the species that were dominant in the diet of , ± SE  tin– and –, respectively. Socotra cormorants (MOEW, ; Table ).

TABLE 1 Population size of Socotra cormorants Phalacrocorax nigrogularis on Siniya Island, Umm Al Quwain, United Arab Emirates (Fig. ), and the estimated biomass consumed by the population during the – and – breeding seasons.

Non-breeding Breeding Breeding season Chicks Fledged chicks Juveniles adults adults Total Population size (no. of individuals ± SE) 2011–2012 40,157 ± 1,606 26,343 ± 1,053 12,950 ± 730 6,981 ± 411 56,644 ± 3641 102,919 ± 665 2012–2013 82,210 ± 2,844 67,412 ± 2,332 17,388 ± 980 9,374 ± 553 75,602 ± 7602 169,776 ± 1,401 Tonnes of fish biomass consumed ± SE 2011–2012 808 ± 32 2,343 ± 93 1,439 ± 101 776 ± 57 6,260 ± 50 11,626 ± 72 2012–2013 1,491 ± 51 5,960 ± 206 1,921 ± 135 1,036 ± 76 8,356 ± 105 18,764 ± 126

 , breeding pairs  , breeding pairs

Discussion parents provided approximately the same amount of food to their growing chicks, compensating for differences in the – Cormorant fisheries interactions remain a contentious issue biomass of individual fish species. As partly digested fish in wildlife management. Increases in populations of great were not included in the analyses, rare species were probably cormorants Phalacrocorax carbo are usually met with aggres- not adequately sampled and only dominant species were sive management intervention, primarily to protect fisheries quantified, and therefore further studies are needed to char-   (Vetemaa et al., ; Emmrich & Düttman, ). Fine-scale acterize the breadth of the diet of cormorants. studies have helped to refute or confirm the suspected nega- Many cormorant species exhibit opportunistic dietary pat- tive impact of cormorants on fisheries (Van Eerden et al., ternsoverthecourseofayear(Nelson,;Liordos&    ; Vetemaa et al., ; Emmrich & Düttman, ). The Goutner, ), suggesting adaptability to changing fish Arabian Gulf has a relatively small volume and is semi- stocks. Jennings () reported that sardines, halfbeaks, isolated, with a species-poor fish fauna derived from the ad- scads and rabbitfish formed part of the diet of Socotra cormor-   jacent Arabian Sea (Sheppard, ;Grandcourt, ). ants in the Hawar Islands in Bahrain. Although these species Commercial fishing in the Arabian Gulf has increased in were not recorded in our study, some are from the same fam- recent years as a result of development in the Middle East ilies (pelagic species of Hemiramphidae, Clupeidae and   (Grandcourt, ;Jabado, ), and is dominated by Carangidae). This indicates that cormorants from different col- – medium large reef fish species belonging to the Serranidae, onies may have dissimilar diets, depending on the available Sparidae, Lethrinidae, Lutjanidae and Carangidae local fish resources, seasonality and year, although the major    (Carpenter et al., ; EAD, ; Grandcourt, ). fish groups targeted may be similar. Intercolony variation in The breeding population of Socotra cormorants of Siniya diet has been widely reported in other cormorant (Liordos & Island may have a significant impact on its food webs, utilizing Goutner, ) and seabird species (Schreiber & Burger, ) – a variety of small fish of length mm. The diet of chicks and requires further investigation in Socotra cormorants. varied significantly between years, suggesting that the species is Mean biomass of fish load increased significantly during a generalist, feeding opportunistically on abundant fish species. the latter part of the – season. This was probably a The local fisheries primarily land large demersal or reef fishes, reflection of the breeding phase, with larger chicks compel- whereas the diet of cormorant chicks consists of small, pelagic ling parents to provide larger fish loads. The change in fish fishes, mostly of low commercial value, and therefore the im- biomass also reflected a switch from mainly flying fish to pact of the cormorants on fisheries is minimal. sardines, as parents provided more nutritious food to their growing chicks (Barati, ; Emmrich & Düttmann, ). Chick diet The diets of great cormorants are also known to change in response to the nutritional requirements of growing chicks Socotra cormorants appear to be a generalist species, with during the course of a season (Liordos & Goutner, ; significant variation in the diet of chicks. The diet consisted Barati, ; Emmrich & Düttmann, ). mostly of sailfin flying fish and blue-stripe sardines in – In contrast, in – the biomass of fish loads declined  and anchovies in –. The fishes consumed were as the season progressed. A larger sample size could have pro- small (biomass – g), with significantly lower individual vided a better understanding of how fish loads change in rela- biomass recorded in –, when anchovies comprised tion to fish availability; however, we speculate that difference in % of the diet. The mean biomass of fish loads was not sig- the timing of breeding between – and – could nificantly different between years, however, indicating that explain our observations. In – breeding started c. 

TABLE 2 Overlap between major fish species targeted commercially that although great cormorant populations were linked or as baitfish and the diet of Socotra cormorants on Siniya Island, with fish densities, predation pressure from cormorants  United Arab Emirates (Fig. ). did not cause a decline in fish densities in Lake Ymsen, Cormorant Sweden. Thus, the perceived impact of cormorants on fish- Species Fishery diet eries is often incorrect. Troynikov et al. () showed that Carnagidae great cormorants selected fish of size classes that did not Carangoides bajad Commercial overlap with the fish targeted by the European perch Selar crumenophthalmus Minor Perca fluviatilis fishery in Lithuania. Furthermore, great cor- component morants may select different species from those targeted by Haemulidae fisheries in Greece (e.g. Liordos & Goutner, ). The fish Scomberoides commersonnianus Commercial landings of the United Arab Emirates have been increasing Diagramma pictum Commercial steadily since the s (Beech et al., ; Grandcourt, Lethrinidae  Lethrinus lentjan Commercial Minor ). The fisheries statistics reports for the emirate of component Abu Dhabi suggests that the bulk of the fish catch comprises Lethrinus nebulosus Commercial orange-spotted trevally Carangoides bajad, Talang queen- Portunidae fish Scomberoides commersonnianus, painted sweetlips Portunus pelagicus Commercial Diagramma pictum, pink ear emperor, spangled emperor Scombridae Lethrinus nebulosus, blue crab Portunus pelagicus, narrow- Scomberomorus commerson Commercial barred Spanish mackerel Scomberomorus commerson, Serranidae Epinephelus coidoides Commercial orange-spotted grouper Epinephelus coioides and pickhan- .    Sphyraenidae dle barracuda (collectively , t per year, % of total Sphyraena jello Commercial Minor catch in Abu Dhabi in ; EAD, b). Similar data for component other emirates are not available but it may be assumed Engraulidae that they exploit similar species, given the widespread popu- Encrasicholina spp. Baitfish Major larity of these species (Beech et al., ; Grandcourt, ). component The sailfin flying fish, which comprised .% of the diet of Clupeidae – Sardinella longiceps Baitfish Socotra cormorants in , is not exploited by the Herklotsichthys quadrimaculatus Major fishery, and the blue-stripe sardine, which dominated the component diet (.%), is exploited for consumption, baitfish or animal Exocetidae feed but is not reported in the fisheries statistics Parexocoetus mento Major (Grandcourt, ; EAD, a; MOEW, ). Similarly, component anchovies, which dominated the Socotra cormorant’s diet Hemiramphidae in – (.%), are used as baitfish or animal feed Hyporhamphus limbatus Minor but their exploitation is not of commercial importance. It component is possible that Socotra cormorants may influence commercial fish species indirectly by eating younger individuals or weeks later and peak breeding was observed in December, the prey of the larger fish. Our study does not provide evi- – compared to November in .Anchoviesinthe dence of significant consumption of any larval stages of Arabian Gulf migrate westwards from the northern emirates commercially important fish. The two commercially (including Umm Al Quwain) in December and become less exploited species found in the diet, S. jello and L. lenjtans, abundant after January (MOEW, pers. comm.). Thus, a constituted minor components of the diet. Selar crume- – more prolonged breeding season in could have nophthalmus is not reported in the fisheries statistics, al- caused a decline in the local stocks of anchovies, which was re- though other species of scads (e.g. Atule bajad)are flected in the lower biomass of fish loads observed late in the targeted at low levels (,  t annually; EAD, ) by the season. A more detailed investigation of seasonal changes in commercial fishery. Anchovies were the most important diet is necessary to better understand dietary shifts in breeding component of the diet in the – breeding season, colonies of Socotra cormorants. suggesting that there could be conflict between cormorants and fishers. However, species that are considered baitfish Impact on fisheries (e.g. Sardinella longiceps, Encrasicholina spp.) seem to be captured opportunistically and at sufficiently low levels Great cormorants have contrasting impacts on local fish re- that they are not reported in the fishery statistics (EAD, sources. Increasing populations caused a decline in fish a; MOEW, ). Reports of fishers’ attitudes towards stocks in an estuary in Estonia over a -year period Socotra cormorants are anecdotal, and formal surveys are (Vetemaa et al., ). However, Engström () showed needed to determine perceptions and attitudes of fishers.

The total quantity of fish consumed by the Socotra cor- Norway and possible implications for gadoid stock recruitment. morant population breeding on Siniya Island is small com- Marine Ecology Progress Series, , –.  pared to the total tonnage of exploited species (MOEW, BEECH, M., AL ABDUSSALAM,T.&HOOLIHAN, J.P. ( ) Marine   fish. In Emirates: A Natural History (eds P. Hellyer & S. Aspinall), ; Table ). Juveniles and breeding and non-breeding pp. –. Trident Press, Abu Dhabi, United Arab Emirates. adults leave the colony to disperse as far as Abu Dhabi in BIRDLIFE INTERNATIONAL () Phalacrocorax nigrogularis.InThe the west and across the Strait of Hormutz into the Gulf of IUCN Red List of Threatened Species v. .. Http://www. Oman in the east (Muzaffar, ), thus they forage away iucnredlist.org [accessed  September ].  from the breeding colony during April–September, exploit- CARPENTER, K.E., KRUPP, F., JONES, D.A. & ZAJONZ,U.( ) FAO Species Identification Guide for Fishery Purposes. The Living Marine ing other regions of the Gulf. Based on the little overlap be- Resources of Kuwait, Eastern Saudi Arabia, Bahrain, Qatar, and the tween the diet of cormorant chicks and commercially United Arab Emirates. Food and Agriculture Organization of the exploited species, and the relatively small biomass con- United Nations, Rome, Italy. sumed by cormorants, we suggest that the species has a CRAMP,S.() Handbook of the Birds of Europe, the Middle East, and low impact on the commercial fisheries of the United North Africa: The Birds of the Western Palearctic. Oxford University Press, Oxford, UK. Arab Emirates. The negative perception among fishers of DALTON, C.M., ELLIS,D.&POST, D.M. () The impact of the effects of cormorants on fish stocks in the United double-crested cormorant (Phalacrocorax auritus) predation on Arab Emirates or the greater Arabian Gulf is misplaced. anadromous alewife (Alosa pseudoharengus) in south-central Measures must be taken to ensure sustainability of fish- Connecticut, USA. Canadian Journal of Fisheries and Aquatic  – eries and to protect the Socotra cormorant, especially on Sciences, , . DANCKWERTS, D.K., MCQUAID, C.D., JAEGER, A., MCGREGOR, G.K., Siniya Island. As the United Arab Emirates hosts %of DWIGHT, R., LE CORRE,M.&JAQUEMET,S.() Biomass the global population of the species, protection and better consumption by breeding seabirds in the western Indian Ocean: understanding of Siniya Island and other colonies in Abu indirect interactions with fisheries and implications for Dhabi are essential. Siniya Island hosts the largest popula- management. ICES Journal of Marine Science. Http://dx.doi.org/. tion of breeding Socotra cormorants in the United Arab /icesjms/fsu.  Emirates (Jennings, ). Long-term studies examining EMMRICH,M.&DÜTTMANN,H.( ) Seasonal shifts in diet composition of great cormorants Phalacrocorax carbo sinensis diet of this and other seabird species will help to understand foraging at a shallow eutrophic inland lake. Ardea, , –. the role of Socotra cormorants and other seabirds in shaping ENGSTRÖM,H.() Long term effects of cormorant predation on fish the food webs of the Arabian Gulf. communities and fishery in a freshwater lake. Ecography, , –. EAD () Annual Report. Environment Agency–Abu Dhabi, United Arab Emirates. EAD (a) Annual Fisheries Statistics Report for Abu Dhabi Emirate Acknowledgements . Terrestrial and Marine Biodiversity Sector, Environment Agency–Abu Dhabi, United Arab Emirates. We thank the Ministry of Environment and Water for pro- EAD (b) Annual Report. Environment Agency–Abu Dhabi, viding funding to SBM and logistical support for this work. United Arab Emirates. Additional support for the project was received through the FAO () FAO Species Identification Sheets for Fishery Purposes. Mohammad Bin Zayed Species Conservation Fund and the Eastern Indian Ocean Fishing Area  and Western Central Pacific  United Arab Emirates University/National Research Fishing Area . Food and Agriculture Organization of the United Nations, Rome, Italy. Foundation grant to SBM. We thank the Umm Al FROESE,R.&PAULY, D. (eds) () FishBase. Http://www.fishbase. Quwain Municipality for issuing permits to work on the is- org [version (/)]. land. All field procedures adhere to international standards GLAHN, J.F. & BRUGGER, K.E. () The impact of double-crested that were approved by the Animal Research Ethics cormorants on the Mississippi Delta catfish industry: a bioenergetics Committee (Protocol No. A-) of UAE University, the model. 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ICES Journal of Marine Science, cormorant (Phalacrocorax nigrogularis) in the eastern Arabian Gulf. , –. In Seabirds and Songbirds: Ecology, Conservation and Migratory WESELOH, D.V., EWINS, P.J., STRUGER, J., MINEAU, P., BISHOP, C.A., Behavior (ed. G. Mahala), pp. −. Nova Science Publishers, POSTUPALSKY,S.&LUDWIG, J.P. () Double-crested cormorants Inc., New York, USA. of the Great Lakes: changes in population size, breeding distribution MUZAFFAR, S.B., GUBIANI,R.&BENJAMIN,S.() Reproductive and reproductive output between  and . Colonial performance of the Socotra cormorant (Phalacrocorax nigrogularis) Waterbirds, , –. on Siniya Island, United Arab Emirates: planted trees increase WILSON, K.D.P. () Breeding of Socotra cormorant at Umm Qasr hatching success. Waterbirds, , –. Island. The Phoenix, , –. MUZAFFAR, S.B., BENJAMIN,S.&GUBIANI,R.() The impact of ZIJLSTRA,M.&VAN EERDEN, M.R. () Pellet production and the fox and feral cat predation on the population viability of the use of otoliths in determining the diet of cormorants Phalacrocorax threatened, endemic Socotra cormorant on Siniya Island, United carbo sinensis: trials with captive birds. Ardea, , –. Arab Emirates. Marine Ornithology, , –. MUZAFFAR, S.B., GUBIANI,R.&BENJAMIN,S.() Nest location influences hatching success in the Socotra cormorant Biographical sketches (Phalacrocorax nigrogularis) on Siniya Island, United Arab Emirates. Wildlife Research, , –. SABIR BIN MUZAFFAR’s research focuses on the movement ecology, NAGY, K.A. () Field metabolic rate and food requirement scaling breeding biology and conservation of birds. ROBERT GUBIANI in mammals and birds. Ecological Monographs, , –. works on a variety of environmental projects relating to biodiversity NELSON, J.B. () Pelicans, Cormorants and their Relatives: The and conservation. SONYA BENJAMIN’s research interests focus on de- Pelecaniforms. Oxford University Press, Oxford, UK. termining the effectiveness of common ecological mitigation measures NETTLESHIP, D.N. & DUFFY, D.C. () Cormorants and human often proposed as a means of alleviating adverse impacts from devel- interactions: an introduction. Colonial Waterbirds, , –. opmental pressures in the Middle East. RASHID AL SHIHI’s research ÖSTMAN, Ö., BOSTRÖM, M.K., BERGSTRÖM, U., ANDERSSON,J.& interests focus on marine organisms, including sea birds, and marine LUNNERYD, S.-G. () Estimating competition between wildlife ecosystems and conservation. AHMED AL -ROMITHI has worked on and humans—a case of cormorants and coastal fisheries in the Baltic the diet and foraging of cormorants. FAISAL AL KAABI is interested Sea. PLoS ONE, (), e. in the feeding ecology of cormorants.