Minton, Gianna,van Bressem, M. F.,Willson, A.,Collins, T.,Al Harthi, S.,Sarrouf Willson, M.,Baldwin, R.,Leslie, M.,Robbins, J.,Van Waerebeek, K
Visual Health Assessment and evaluation of Anthropogenic threats to Arabian Sea Humpback Whales in Oman Technical Report
Document presented to the Scientific Committee of the International Whaling Commission no. 418, 2020.
Abstract | Links | BibTeX | Tags: Arabian Sea, Barnacle, Bycatch, disease, Fisheries, Humpback Whale, killer whale, lesions, megaptera novaeangliae, Oman, pathology, photo identification, predation, scarring, skin, tattoo
@techreport{,
title = {Visual Health Assessment and evaluation of Anthropogenic threats to Arabian Sea Humpback Whales in Oman},
author = {Minton, Gianna,van Bressem, M. F.,Willson, A.,Collins, T.,Al Harthi, S.,Sarrouf Willson, M.,Baldwin, R.,Leslie, M.,Robbins, J.,Van Waerebeek, K},
url = {https://arabianseawhalenetwork.org/wp-content/uploads/2020/06/sc_68b_cmp_16_rev1_visual-health-assessment-of-ashw-in-oman-1.pdf},
year = {2020},
date = {2020-01-01},
journal = {Paper presented to the meeting of the Scientific Committee of the International Whaling Commission},
number = {418},
pages = {25},
publisher = {IWC},
institution = {Document presented to the Scientific Committee of the International Whaling Commission},
abstract = {Arabian Sea humpback whales have been a subject of conservation concern in the IWC since 1997. Research conducted primarily off the coast of Oman has contributed to understanding the population’s distribution, abundance, and conservation status, whilst information on the population’s health and specific threats is more limited. This study examines all available images of Arabian Sea humpback whales obtained between 2000 and 2018 for evidence of disease, predation, epizoites and human-induced scarring or injury to individuals. Tattoo-like skin disease was detected in 43.4% of 83 adult whales, with a roughly equal distribution between males and females. The prevalence of the disease was significantly higher in 2012-2018 (51.7%) than in 2000-2011 (24.1%). The lesions persisted for two to 14 years in 10 whales and progressed in prevalence and percentage of body cover in six of them. Killer whale tooth rakes were detected in 12% (95% CI 4.5-18%) of individuals based on examination of photographs showing the ventral surface of tail flukes (n=77), but no cookie cutter shark wounds were detected on any body parts of any of the whales examined. Roughly two thirds (66.6%: 95% CI 52-80%) of individuals represented by good quality photos of the caudal peduncle region (n=42) bore scarring patterns considered likely to be associated with entanglement in fishing gear, with no significant differences in entanglement scarring rates between males and females. Four individuals bore injuries consistent with vessel strikes and at least two individuals showed severe injuries and deformations likely to have been caused by interactions with vessels and/or fishing gear. Five documented entanglement events from Oman and Pakistan involved large-mesh nylon gillnets, which are known to be used extensively throughout the Arabian Sea. In light of this population’s endangered status, these findings indicate an urgent need to continue monitoring Arabian Sea humpback whales, with an emphasis on methods that allow continued and expanded assessment of health, body condition, and anthropogenic interactions, aimed toward designing effective conservation strategies to mitigate known threats. },
keywords = {Arabian Sea, Barnacle, Bycatch, disease, Fisheries, Humpback Whale, killer whale, lesions, megaptera novaeangliae, Oman, pathology, photo identification, predation, scarring, skin, tattoo},
pubstate = {published},
tppubtype = {techreport}
}
Arabian Sea humpback whales have been a subject of conservation concern in the IWC since 1997. Research conducted primarily off the coast of Oman has contributed to understanding the population’s distribution, abundance, and conservation status, whilst information on the population’s health and specific threats is more limited. This study examines all available images of Arabian Sea humpback whales obtained between 2000 and 2018 for evidence of disease, predation, epizoites and human-induced scarring or injury to individuals. Tattoo-like skin disease was detected in 43.4% of 83 adult whales, with a roughly equal distribution between males and females. The prevalence of the disease was significantly higher in 2012-2018 (51.7%) than in 2000-2011 (24.1%). The lesions persisted for two to 14 years in 10 whales and progressed in prevalence and percentage of body cover in six of them. Killer whale tooth rakes were detected in 12% (95% CI 4.5-18%) of individuals based on examination of photographs showing the ventral surface of tail flukes (n=77), but no cookie cutter shark wounds were detected on any body parts of any of the whales examined. Roughly two thirds (66.6%: 95% CI 52-80%) of individuals represented by good quality photos of the caudal peduncle region (n=42) bore scarring patterns considered likely to be associated with entanglement in fishing gear, with no significant differences in entanglement scarring rates between males and females. Four individuals bore injuries consistent with vessel strikes and at least two individuals showed severe injuries and deformations likely to have been caused by interactions with vessels and/or fishing gear. Five documented entanglement events from Oman and Pakistan involved large-mesh nylon gillnets, which are known to be used extensively throughout the Arabian Sea. In light of this population’s endangered status, these findings indicate an urgent need to continue monitoring Arabian Sea humpback whales, with an emphasis on methods that allow continued and expanded assessment of health, body condition, and anthropogenic interactions, aimed toward designing effective conservation strategies to mitigate known threats.
Ponnampalam, L.
No Danger in Sight? An Observation of Sperm Whales (Physeter macrocephalus) in Marguerite Formation off Muscat, Sultanate of Oman Journal Article
In: Aquatic Mammals, vol. 42, no. 432, pp. 162-167, 2016.
Abstract | BibTeX | Tags: bottlenose dolphin, Grampus griseus, Interspecies interactions, Oman, Physeter macrocephalus, predation, Risso's dolphin, Social behaviour, sperm whale, tursiops sp
@article{,
title = {No Danger in Sight? An Observation of Sperm Whales (Physeter macrocephalus) in Marguerite Formation off Muscat, Sultanate of Oman},
author = {Ponnampalam, L.},
year = {2016},
date = {2016-01-01},
journal = {Aquatic Mammals},
volume = {42},
number = {432},
pages = { 162-167},
abstract = {The note documents a sperm whale encounter off Muscat where roughly 35 individuals formed a marguerite but not in response to any obvious threat or danger. Bottlenose dolphins and rissos dolphins were present.},
keywords = {bottlenose dolphin, Grampus griseus, Interspecies interactions, Oman, Physeter macrocephalus, predation, Risso's dolphin, Social behaviour, sperm whale, tursiops sp},
pubstate = {published},
tppubtype = {article}
}
The note documents a sperm whale encounter off Muscat where roughly 35 individuals formed a marguerite but not in response to any obvious threat or danger. Bottlenose dolphins and rissos dolphins were present.
Ashjian,C.J.,Smtih,S.L.,Flagg,C.N.,Idrisi,N.
Distribution, annual cycle, and vertical migration of acoustically derived biomass in the Arabian Sea during 1994-1995 Journal Article
In: Deep-Sea Research Part II, vol. 49, no. 299, pp. 2377-2402, 2002.
Abstract | BibTeX | Tags: acoustic, Arabian Sea, diel, Distribution, history, life history, migration, myctophids, Oceanic, Oman, predation, seasonal change, stocks, Upwelling, zooplankton
@article{,
title = {Distribution, annual cycle, and vertical migration of acoustically derived biomass in the Arabian Sea during 1994-1995},
author = {Ashjian,C.J.,Smtih,S.L.,Flagg,C.N.,Idrisi,N.},
year = {2002},
date = {2002-01-01},
journal = {Deep-Sea Research Part II},
volume = {49},
number = {299},
pages = {2377-2402},
abstract = {The distinguishing characteristic that sets the Arabian Sea apart from other oceanic regions is the regular oscillation of monsoonal atmospheric conditions that produces predictable periods of upwelling or convective mixing, with associated biological response, during the Southwest and Northeast monsoons, respectively. This oscillation is also evident in cycles of standing stocks of zooplankton and micronekton. The vertical distribution and spatial pattern of zooplankton and micronekton biomass were estimated using an acoustic Doppler current profiler along a 1000-km transect extending from the continental shelf of Oman to the central Arabian Sea during ten cruises on the R/V Thomas G. Thompson (November 1994-December 1995). The influence of the Southwest Monsoon, and accompanying upwelling and enhanced acoustically derived biomass, was the dominant feature in the spatial-temporal distributions of both zooplankton and micronekton near the Omani coast. The diel vertical migration of predators (myctophids, pelagic crabs), and the seasonal changes in the strength of this signal, was the most significant pattern observed in the vertical distribution of biomass and imparted a strong day-night signal to the integrated upper water-column biomass. Significant differences in the magnitude of integrated upper water-column biomass, both zooplankton (day) and migrator-zooplankton (night), were seen between inshore and offshore of the atmospheric Findlater Jet. A station located in the central Arabian Sea demonstrated seasonal changes in biomass over the year, despite being quite far from the influence of the monsoonal oscillations. Predation pressure was greater offshore of the Findlater Jet than in the region inshore of the Jet or in the central Arabian Sea. The pelagic community of the Arabian Sea may have evolved life history strategies to coincide with the predictable monsoonal cycle},
keywords = {acoustic, Arabian Sea, diel, Distribution, history, life history, migration, myctophids, Oceanic, Oman, predation, seasonal change, stocks, Upwelling, zooplankton},
pubstate = {published},
tppubtype = {article}
}
The distinguishing characteristic that sets the Arabian Sea apart from other oceanic regions is the regular oscillation of monsoonal atmospheric conditions that produces predictable periods of upwelling or convective mixing, with associated biological response, during the Southwest and Northeast monsoons, respectively. This oscillation is also evident in cycles of standing stocks of zooplankton and micronekton. The vertical distribution and spatial pattern of zooplankton and micronekton biomass were estimated using an acoustic Doppler current profiler along a 1000-km transect extending from the continental shelf of Oman to the central Arabian Sea during ten cruises on the R/V Thomas G. Thompson (November 1994-December 1995). The influence of the Southwest Monsoon, and accompanying upwelling and enhanced acoustically derived biomass, was the dominant feature in the spatial-temporal distributions of both zooplankton and micronekton near the Omani coast. The diel vertical migration of predators (myctophids, pelagic crabs), and the seasonal changes in the strength of this signal, was the most significant pattern observed in the vertical distribution of biomass and imparted a strong day-night signal to the integrated upper water-column biomass. Significant differences in the magnitude of integrated upper water-column biomass, both zooplankton (day) and migrator-zooplankton (night), were seen between inshore and offshore of the atmospheric Findlater Jet. A station located in the central Arabian Sea demonstrated seasonal changes in biomass over the year, despite being quite far from the influence of the monsoonal oscillations. Predation pressure was greater offshore of the Findlater Jet than in the region inshore of the Jet or in the central Arabian Sea. The pelagic community of the Arabian Sea may have evolved life history strategies to coincide with the predictable monsoonal cycle
Butler,M.,Bollens,S.M.,Burghalter,B.,Madin,L.P.,Horgan,E.
Mesopelagic fishes of the Arabian Sea: distribution, abundance and diet of Journal Article
In: Deep-Sea Research Part II, vol. 48, no. 61, pp. 1369-1383, 2001.
Abstract | BibTeX | Tags: abundance, Arabian Sea, diel, diet, diets, Distribution, ecology, feeding, migration, oxygen minimum, population, populations, predation, south
@article{,
title = {Mesopelagic fishes of the Arabian Sea: distribution, abundance and diet of },
author = {Butler,M.,Bollens,S.M.,Burghalter,B.,Madin,L.P.,Horgan,E.},
year = {2001},
date = {2001-01-01},
journal = {Deep-Sea Research Part II},
volume = {48},
number = {61},
pages = {1369-1383},
abstract = {Four species of predatory fishes - Chauliodus pammelas, Chauliodus sloani, Stomias afffnis and Stomias nebulosus - were collected on two cruises to the Arabian Sea during 1995. We present data on the abundances, horizontal and vertical distributions, and diet of these fishes. We also discuss briefly the importance of the oxygen minimum zone and predation on myctophid fishes to the ecology of these mesopelagic predators. Chauliodus pammelas and C. sloani appear to have only partially overlapping horizontal distributions in the Arabian Sea, with C. pammelas more common to the north and C. sloani more common to the south. Our data support previous results suggesting that diel vertical migration is the norm for these species, with smaller individuals usually nearer to the surface and larger individuals tending to stay deeper. In contrast to Chauliodus, Stomias affinis and S. nebulosus appear to have largely overlapping horizontal distributions in the Arabian Sea. However, they may have slightly di!erent vertical distributions, with S. affinis living slightly shallower (especially at night) than S. nebulosus. All four species spend most of their time in the oxygen minimum zone, entering the surface oxygenated waters (100-150 m) only at night (if at all). The diets of C. pammelas, C. sloani, and S. affinis consisted mainly of lantern fishes, Myctophidae, and other fishes. In contrast, S. nebulosus, the smaller of the two Stomias species, ate mostly copepods and other crustaceans. This differential feeding may allow the two Stomias species to co-occur. Three of these four stomiids appear to play an important role in predation on myctophid fish populations in the Arabian Sea.},
keywords = {abundance, Arabian Sea, diel, diet, diets, Distribution, ecology, feeding, migration, oxygen minimum, population, populations, predation, south},
pubstate = {published},
tppubtype = {article}
}
Four species of predatory fishes - Chauliodus pammelas, Chauliodus sloani, Stomias afffnis and Stomias nebulosus - were collected on two cruises to the Arabian Sea during 1995. We present data on the abundances, horizontal and vertical distributions, and diet of these fishes. We also discuss briefly the importance of the oxygen minimum zone and predation on myctophid fishes to the ecology of these mesopelagic predators. Chauliodus pammelas and C. sloani appear to have only partially overlapping horizontal distributions in the Arabian Sea, with C. pammelas more common to the north and C. sloani more common to the south. Our data support previous results suggesting that diel vertical migration is the norm for these species, with smaller individuals usually nearer to the surface and larger individuals tending to stay deeper. In contrast to Chauliodus, Stomias affinis and S. nebulosus appear to have largely overlapping horizontal distributions in the Arabian Sea. However, they may have slightly di!erent vertical distributions, with S. affinis living slightly shallower (especially at night) than S. nebulosus. All four species spend most of their time in the oxygen minimum zone, entering the surface oxygenated waters (100-150 m) only at night (if at all). The diets of C. pammelas, C. sloani, and S. affinis consisted mainly of lantern fishes, Myctophidae, and other fishes. In contrast, S. nebulosus, the smaller of the two Stomias species, ate mostly copepods and other crustaceans. This differential feeding may allow the two Stomias species to co-occur. Three of these four stomiids appear to play an important role in predation on myctophid fish populations in the Arabian Sea.
Corkeron,P.J.,Connor,R.C.
Why do baleen whales migrate? Journal Article
In: Marine Mammal Science, vol. 15, no. 76, pp. 1228-1245, 1999.
Abstract | BibTeX | Tags: abundance, Distribution, killer whale, killer whales, migration, mysticetes, Orca, predation
@article{,
title = {Why do baleen whales migrate?},
author = {Corkeron,P.J.,Connor,R.C.},
year = {1999},
date = {1999-01-01},
journal = {Marine Mammal Science},
volume = {15},
number = {76},
pages = {1228-1245},
abstract = {The annual migrations of baleen whales are a conspicuous, but unexplained feature of their behavioural repertoire. Some hypotheses offered to explain whale migration focus on direct benefits to the calf (thermoregulation, calm water) and some do not (resource tracking, and the "evolutionary holdover" hypothesis). Here we suggest that a major selective advantage to migrating pregnant female baleen whales is a reduced risk of killer whale predation on their newborn calves in low-latitude waters. Killer whale abundance in high latitudes is substantially greater than that in lower latitudes, and most killer whales do not appear to migrate with baleen whales. We suggest that the distribution of killer whales is determined more by their primary marine mammal prey, pinnipeds, and that following the baleen whale migrations would remove them from their pinnipeds prey. There are problems with all current hypotheses, most of which stem from a lack of directed research. We explore variation in migratory habits between species, populations, and individuals that may provide a "natural laboratory" for discriminating among the competing hypotheses. The authors specifically recommend more detailed study of non-migrating populations, such as the Arabian Sea population of humpback whales.},
keywords = {abundance, Distribution, killer whale, killer whales, migration, mysticetes, Orca, predation},
pubstate = {published},
tppubtype = {article}
}
The annual migrations of baleen whales are a conspicuous, but unexplained feature of their behavioural repertoire. Some hypotheses offered to explain whale migration focus on direct benefits to the calf (thermoregulation, calm water) and some do not (resource tracking, and the "evolutionary holdover" hypothesis). Here we suggest that a major selective advantage to migrating pregnant female baleen whales is a reduced risk of killer whale predation on their newborn calves in low-latitude waters. Killer whale abundance in high latitudes is substantially greater than that in lower latitudes, and most killer whales do not appear to migrate with baleen whales. We suggest that the distribution of killer whales is determined more by their primary marine mammal prey, pinnipeds, and that following the baleen whale migrations would remove them from their pinnipeds prey. There are problems with all current hypotheses, most of which stem from a lack of directed research. We explore variation in migratory habits between species, populations, and individuals that may provide a "natural laboratory" for discriminating among the competing hypotheses. The authors specifically recommend more detailed study of non-migrating populations, such as the Arabian Sea population of humpback whales.
Smith,S.,Roman,M.,Prusova,I.,Wishner,K.,Gowing,M.,Codispoti,L.A.,Barber,R.,Marra,J.,Flagg,C.
Seasonal response of zooplankton to monsoonal reversals in the Arabian Sea Journal Article
In: Deep-Sea Research Part II, vol. 45, no. 478, pp. 2369-2403, 1998.
Abstract | BibTeX | Tags: Arabian Sea, Distribution, migration, predation, Upwelling, zooplankton
@article{,
title = {Seasonal response of zooplankton to monsoonal reversals in the Arabian Sea},
author = {Smith,S.,Roman,M.,Prusova,I.,Wishner,K.,Gowing,M.,Codispoti,L.A.,Barber,R.,Marra,J.,Flagg,C.},
year = {1998},
date = {1998-01-01},
journal = {Deep-Sea Research Part II},
volume = {45},
number = {478},
pages = {2369-2403},
abstract = {The US JGOFS Arabian Sea Process Study was designed to provide a seasonally and spatially resolved carbon budget for a basin exhibiting some of the highest and lowest concentrations of plant biomass in the world's ocean. During the US JGOFS Process Study in the Arabian Sea (September 1994-January 1996), the absolute maximum in biomass of epipelagic zooplankton in the entire study was observed during the Southwest Monsoon season inshore of the Findlater Jet in the area of upwelling. The greatest contrast between high and low biomass in the study area also was observed during the Southwest Monsoon, as was the strongest onshore-offshore gradient in biomass. Lowest biomass throughout the study was observed at the most offshore station (SI5), outside the direct influence of the monsoon forcing. The greatest day/night contrastsing biomass were observed nearshore in all seasons, with nighttime biornass-exceeding daytime in the Northeast Monsoon season, but daytime exceeding nighttime in the Southwest Monsoon season. The diel vertical migration patterns in general reversed between the monsoons at all stations in the southern part of the study area. Virtually, no diel vertical migration of zooplankton took place in any season at the station with strong, persistent subsurface suboxic conditions (N7), suggesting that these conditions suppress migration. Based on the distribution of biomass, we hypothesize that inshore of the Findlater Jet, zooplankton grazing on phytoplankton is the dominant pathway of carbon transformation during both monsoon seasons, whereas offshore the zooplankton feed primarily on microplankton or are carnivorous, conditions that result in reduction of the carbon flux mediated by the zooplankton. Predation by mesopelagic fish., primarily myctophids, may equal daily growth of zooplankton inshore of the Findlater Jet during all seasons. This suggests that the food web inshore of the Findlater Jet is well integrated, may have evolved during past periods of intensified upwelling, and has a distinctly annual cycle. (C) 1998 Elsevier Science Ltd. All rights reserved.},
keywords = {Arabian Sea, Distribution, migration, predation, Upwelling, zooplankton},
pubstate = {published},
tppubtype = {article}
}
The US JGOFS Arabian Sea Process Study was designed to provide a seasonally and spatially resolved carbon budget for a basin exhibiting some of the highest and lowest concentrations of plant biomass in the world's ocean. During the US JGOFS Process Study in the Arabian Sea (September 1994-January 1996), the absolute maximum in biomass of epipelagic zooplankton in the entire study was observed during the Southwest Monsoon season inshore of the Findlater Jet in the area of upwelling. The greatest contrast between high and low biomass in the study area also was observed during the Southwest Monsoon, as was the strongest onshore-offshore gradient in biomass. Lowest biomass throughout the study was observed at the most offshore station (SI5), outside the direct influence of the monsoon forcing. The greatest day/night contrastsing biomass were observed nearshore in all seasons, with nighttime biornass-exceeding daytime in the Northeast Monsoon season, but daytime exceeding nighttime in the Southwest Monsoon season. The diel vertical migration patterns in general reversed between the monsoons at all stations in the southern part of the study area. Virtually, no diel vertical migration of zooplankton took place in any season at the station with strong, persistent subsurface suboxic conditions (N7), suggesting that these conditions suppress migration. Based on the distribution of biomass, we hypothesize that inshore of the Findlater Jet, zooplankton grazing on phytoplankton is the dominant pathway of carbon transformation during both monsoon seasons, whereas offshore the zooplankton feed primarily on microplankton or are carnivorous, conditions that result in reduction of the carbon flux mediated by the zooplankton. Predation by mesopelagic fish., primarily myctophids, may equal daily growth of zooplankton inshore of the Findlater Jet during all seasons. This suggests that the food web inshore of the Findlater Jet is well integrated, may have evolved during past periods of intensified upwelling, and has a distinctly annual cycle. (C) 1998 Elsevier Science Ltd. All rights reserved.
Weigmann,R.
On the ecology and feeding habits of the euphausiids (Crustacea) in the Arabian Sea (Zur Okologie und Eranhrungsbiologie der Euphausiaceen (Crustacea) im Arabischen Meer) Journal Article
In: Meteor Forschungsergeb., vol. 5, no. 498, pp. 11-52, 1970.
Abstract | BibTeX | Tags: Arabian Sea, biology, density, diet, Distribution, ecology, Euphausiid, feeding, Gulf of Aden, Gulf of Oman, marine, Oman, population, populations, predation, Red Sea, Upwelling, zooplankton
@article{,
title = {On the ecology and feeding habits of the euphausiids (Crustacea) in the Arabian Sea (Zur Okologie und Eranhrungsbiologie der Euphausiaceen (Crustacea) im Arabischen Meer)},
author = {Weigmann,R.},
year = {1970},
date = {1970-01-01},
journal = {Meteor Forschungsergeb.},
volume = {5},
number = {498},
pages = {11-52},
abstract = {In the present paper, the ecology and feeding habits of euphausiids are described. The samples were taken at the time of the NE-monsoon (1964/65) by R. V. 'Meteor' in the Arabian Sea and adjacent waters. 24 spp were determined. According to distribution of the spp, the following marine areas can be distinguished: Arabian Sea: 24 spp, dominant are Euphausia diomedeae, E. tenera, E. distinguenda, Stylocheiron carinatum. Gulf of Aden: 1 0 spp, dominant are Euphausia diomedeae, E. distinguenda. Red Sea: 6 spp, dominant are Euphausia diomedeae, E. distinguena. Gulf of Oman: 5 spp, dominant are Euphausia distinguenda, Pseudeuphausia latifrons. Persian Gulf: 1 sp- Pseudeuphausia latifrons. The total number of euphausiids indicate the biomass of this group. High densities of euphausiids (200-299 and > 300 individuals/l00 m super(3)) occur in the innermost part of the Gulf of Aden, in the area south of the Euqator near the African east coast, near Karachi (Indian west coast) and in the Persian Gulf. Comparison with data relating to production biology confirms that these are eutrophic zones which coincide with areas in which upwelling occurs at the time of the NE-monsoon. The central part of the Arabian Sea differs from adjacent waters by virtue of less dense euphasiid populations (>199 individuals/lOO m super(3)). Measurements relating to production biology demonstrate a relatively low concentration of primary food sources. Food material was ascertained by analysis of stomach content. The following omnivorous species were examined: Euphausia diomedeae, E. distinguenda, E. tenera, Pseudeuphausia latifronts and Thysanopoda tricuspidata. Apart from crustacean remains large numbers of Foraminifera, Radiolaria, tintinnids, dinoflagellates were found in the stomachs. Quantitatively crustaceans form the most important item in the diet. Food selection on the basis of size an form appears to be restricted to certain genera of tintinnids. The genera Stylocheiron and Nematoscelis are predators. Only crustacean remains were found in the stomachs of Stylocheiron abbreviatum, whereas Radiolaria, Foraminifera and tintinnids occurred to some extent in Nematoscelis sp. Different euphauisiids occupy different positions in the food chain in the Arabian Sea. In omnivorous species the position is variable, since they not only feed by filtering autotrophic and heterotrophic Protista, but also by predation on zooplankton. Carnivorous spp without filtering apparatus feed exclusively on zooolankton of the size of copepods. Only these spp are well established as occupying a higher position in food chain. The parasrtlc protozoan Thalassomyces fagei was found on Euphausia diomedeae, E. tenera, E. distinguenda and E. sanzoi.},
keywords = {Arabian Sea, biology, density, diet, Distribution, ecology, Euphausiid, feeding, Gulf of Aden, Gulf of Oman, marine, Oman, population, populations, predation, Red Sea, Upwelling, zooplankton},
pubstate = {published},
tppubtype = {article}
}
In the present paper, the ecology and feeding habits of euphausiids are described. The samples were taken at the time of the NE-monsoon (1964/65) by R. V. 'Meteor' in the Arabian Sea and adjacent waters. 24 spp were determined. According to distribution of the spp, the following marine areas can be distinguished: Arabian Sea: 24 spp, dominant are Euphausia diomedeae, E. tenera, E. distinguenda, Stylocheiron carinatum. Gulf of Aden: 1 0 spp, dominant are Euphausia diomedeae, E. distinguenda. Red Sea: 6 spp, dominant are Euphausia diomedeae, E. distinguena. Gulf of Oman: 5 spp, dominant are Euphausia distinguenda, Pseudeuphausia latifrons. Persian Gulf: 1 sp- Pseudeuphausia latifrons. The total number of euphausiids indicate the biomass of this group. High densities of euphausiids (200-299 and > 300 individuals/l00 m super(3)) occur in the innermost part of the Gulf of Aden, in the area south of the Euqator near the African east coast, near Karachi (Indian west coast) and in the Persian Gulf. Comparison with data relating to production biology confirms that these are eutrophic zones which coincide with areas in which upwelling occurs at the time of the NE-monsoon. The central part of the Arabian Sea differs from adjacent waters by virtue of less dense euphasiid populations (>199 individuals/lOO m super(3)). Measurements relating to production biology demonstrate a relatively low concentration of primary food sources. Food material was ascertained by analysis of stomach content. The following omnivorous species were examined: Euphausia diomedeae, E. distinguenda, E. tenera, Pseudeuphausia latifronts and Thysanopoda tricuspidata. Apart from crustacean remains large numbers of Foraminifera, Radiolaria, tintinnids, dinoflagellates were found in the stomachs. Quantitatively crustaceans form the most important item in the diet. Food selection on the basis of size an form appears to be restricted to certain genera of tintinnids. The genera Stylocheiron and Nematoscelis are predators. Only crustacean remains were found in the stomachs of Stylocheiron abbreviatum, whereas Radiolaria, Foraminifera and tintinnids occurred to some extent in Nematoscelis sp. Different euphauisiids occupy different positions in the food chain in the Arabian Sea. In omnivorous species the position is variable, since they not only feed by filtering autotrophic and heterotrophic Protista, but also by predation on zooplankton. Carnivorous spp without filtering apparatus feed exclusively on zooolankton of the size of copepods. Only these spp are well established as occupying a higher position in food chain. The parasrtlc protozoan Thalassomyces fagei was found on Euphausia diomedeae, E. tenera, E. distinguenda and E. sanzoi.