Drivers of Cetacean Exploitation: The Case of Ghanaian Coastal Waters in the Gulf of Guinea

The physical habitat of cetaceans found along the continental slope in the north‐central and western Gulf of Mexico was characterized from shipboard sighting data, simultaneous hydrographic measurements, and satellite remote sensing. The study area was encompassed by the longitude of the Florida‐Alabama border (87.5°W), the southernmost latitude of the Texas‐Mexico border (26.0°N), and the 100‐m and 2,000‐m isobaths. Shipboard surveys were conducted seasonally for two years from April 1992 to May 1994. A total of 21,350 km of transect was visually sampled in an area of 154,621 km2.Sighting localities of species in the study area were differentiated most clearly with bottom depth. Atlantic spotted dolphins (Stenella frontalis) were consistently found in the shallowest water on the continental shelf and along the shelf break. In addition, the bottom depth gradient (sea floor slope) was less for Atlantic spotted dolphins than for any other species. Bottlenose dolphins (Tursiops truncatus) were found most commonly along the upper slope in water significantly deeper than that for Atlantic spotted dolphins. All the other species and species categories were found over deeper bottom depths; these were Risso's dolphins (Grampus griseus), short‐finned pilot whales (Glob‐icephala macrorhynchus), pygmy/dwarf sperm whales (Kogia spp.), roughtoothed dolphins (Steno bredanensis), spinner dolphins (Stenella longirostris), sperm whales (Physeter macrocephalus), striped dolphins (Stenella coeruleoalba),Mesoplodonspp., pantropical spotted dolphins (Stenella attenuata), Clymene dolphins (Stenella clymene) and unidentified beaked whales (Ziphiidae). Risso's dolphins and short‐finned pilot whales occurred along the upper slope and, as a subgroup, were significantly different from striped dolphins,Mesoplodonspp., pantropical spotted dolphins, Clymene dolphins, and unidentified beaked whales, which occurred in the deepest water. Pygmy/dwarf sperm whales, rough‐toothed dolphins, spinner dolphins, and sperm whales occurred at intermediate depths between these two subgroups and overlapped them.

The Gulf of Mexico (GMx) is a subtropical marginal sea of the western North Atlantic Ocean with a diverse cetacean community. Ship-based, line-transect abundance surveys were conducted in oceanic waters (>200 m deep) of the northern GMx within U.S. waters (380,432 square km) during summer 2003 and spring 2004. Data from these surveys were pooled and minimum abundance estimates were based on 10,933 km of effort and 433 sightings of at least 17 species.The most commonly sighted species (number of groups) were pantropical spotted dolphin, Stenella attenuata (115); sperm whale, Physeter macrocephalus (85); dwarf/pygmy sperm whale, Kogia sima/breviceps (27); Risso’s dolphin, Grampus griseus (26); and bottlenose dolphin, Tursiops truncatus (26). The most abundant species (number of individuals; coefficient of variation) were S. attenuata (34,067; 0.18); Clymene dolphin, S. clymene (6,575; 0.36); T. truncatus (3,708; 0.42); and striped dolphin, S. coeruleoalba (3,325; 0.48). The only large whales sighted were P. macrocephalus (1,665; 0.20) and Bryde’s whale, Balaenoptera edeni (15; 1.98). Abundances for other species or genera ranged from 57 to 2,283 animals. Cetaceanswere sighted throughout the oceanic northern GMx, and whereas many species were widely distributed, some had more regional distributions. Compared to abundance estimates for this area based on 1996-2001 surveys, the estimate for S. attenuata was significantly smaller (P <0.05) and that for the spinner dolphin, S. longirostris, appeared much smaller. Also, P. macrocephalus estimates were based on less negatively biased estimates of group-size using 90-minute counts during 2003 and 2004.

Stomach content analysis constitutes an important component of fisheries management, providing insight into fish feeding patterns and quantitative assessment of food habits. Thus, a study aimed at obtaining dietary information from stomach contents analysis of the most common by-caught dolphin species, Stenella clymene, beached from the coastal waters of Ghana, along the Gulf of Guinea was undertaken. The stomachs of 39 by-caught clymene dolphins landed at three fisheries landing beaches along the Ghanaian coast, were analyzed. A further study correlating the chemical contaminant load in tissues of Clymene dolphins to that of their preferred prey was undertaken. The stomach contents were generally composed of digested items. Fish, cephalopods and crustaceans were identified and represented a diversity of 12 species. On taxa level, fish was the most frequent (69%) and numerically the most important prey (46.57) followed by cephalopods (3.05) with crustaceans being present in trace amounts (1.55). However, both cephalopods and fish represented a more balanced share of the diet in biomass (45% and 51%) respectively. Thus, clymene dolphins off the coastal waters of Ghana appear to rely principally on both fish and cephalopods for food. Parasites also dominated the gut contents in relative abundance (48.83%). Prey items accumulated chemical contaminants at relatively the same concentrations (50%) as the blubber, liver and muscle of the clymene dolphins, confirming that food is the main source of exposure to contaminant load for marine mammals. With regards to quantitative analysis of prey species of cetaceans, this study of diet in clymene dolphins is the first recorded in this area.

Clymene Dolphin: Stenella clymene

The cetaceans of Ghana and the Gulf of Guinea have, until recently, remained unstudied. Periodical monitoring of artisanal fisheries for bycatches in seven Ghanaian artisanal fishing ports and landing sites over 1996-2004 has provided photographic and specimen evidence to validate occurrence of 18 species (17 odontocetes, 1 mysticete) in a tropical, predominantly pelagic cetacean fauna. At least nine species and subspecies had not previously been documented for Ghana (with asterisk), and four species are authenticated for the first time in the Gulf of Guinea (double asterisk), i.e. Tursiops truncatus, Stenella clymene, S. longirostris longirostris*, S. attenuata, S. frontalis, Delphinus capensis capensis*, Lagenodelphis hosei, Steno bredanensis, Grampus griseus, Peponocephala electra*, Feresa attenuata**, Globicephala macrorhynchus, Orcinus orca*, Pseudorca crassidens*, Kogia sima**, Physetermacrocephalus*, Ziphius cavirostris** and Megaptera novaeangliae . Also, the limited published information on distribution, natural history and conservation status is critically reviewed for each taxon. Indications are that most species encountered off Ghana may be widely distributed in the Gulf of Guinea, most notably the long-beaked common dolphin. The vulnerable Atlantic humpback dolphin, Sousa teuszii, remains unrecorded in Ghana and neighbouring nations despite apparently suitable coastal habitat. It is suggested that localized extinction may be blamed, possibly the result of accumulative bycatches and disturbance. A number of other cetacean species not yet encountered could occasionally occur in Ghana’s waters, e.g. Balaenoptera brydei, Mesoplodon densirostris, Kogia breviceps, Stenella coeruleoalba and Delphinus delphis

One of the largest documented takes of small cetaceans in western Africa occurs in Western regional coastal waters of Ghana. This temporally coincided with steadily decreasing catches of finfish, especially small pelagics (sardinellas, anchovies, mackerel) over the past decades, attributed to both climate change and indiscriminate exploitation methods. Dixcove, a key fishing port for cetacean landings was surveyed during 96 days between 12 September -17 December 2018. Our goal was to update insights from our earlier surveys, especially on catch rates, catch per unit effort and species composition. A total of 57 delphinids of 10 species were observed landed: Stenella attenuata (28.1%), Stenella clymene (17.5%), Lagenodelphis hosei (10.5%), Steno bredanensis (10.5%), unidentified stenellids (8.8%), Grampus griseus (3.5%), Delphinus sp. (3.5%), Pseudorca crassidens (3.5%) and single specimens of Tursiops truncatus, Stenella longirostris and Stenella frontalis. The observed cetacean catch per diem (cpd =0.59) at Dixcove was low compared to earlier rates for this port (e.g. cpd =2.82, in 2013-2014). However, fishing effort, measured as the number of canoes landing per diem (range 0-25; mean= 8.82 ± 6.05; n=22) was also reduced. Poor fish catches forced many canoes to remain in port. The prevalence in landings of common bottlenose dolphins and common dolphins has significantly decreased in the period 2000-2018. The prevalence of Fraser's dolphins and false killer whales increased. Indications are that a higher proportion of cetacean carcasses may be utilised offshore as shark bait. Hooks baited with cetacean parts are deployed in auxiliary longlines set longside large-mesh drift gillnets with a shark aggregating purpose, a first report in Africa. Shore-based incidental sightings of humpback whales suggest the potential for small scale whale-watching ecotourism in Ghanaian coastal waters, as pertains in the nearby waters of the Republic of Benin.

On June 7'h 1995, a young dolphin (genus Stenella) was found dead at 5tella Mares beach (13°00'305; 38°27'20W), Salvador-Bahia. Externai characteristics of this individual suggested that it should be a spinner dolphin, Stenella longirostris. However, because morphometry and color patterns of young Clymene's dolphin, S. clymene, are very similar to S. longirostris the chances of this dolphin being a Clymene's could not be dismissed. In an attempt to confirm the identification of this animal, a 401-bp fragment of the cytochrome b mitochondrial DNA (mtDNA) gene was amplified and sequenced jrom muscle tissue. DNA sequences from 8 other Delphinidae species (Stenella attenuata, S. frontalis, S. longirostris, Steno bredanensis, Sotalia fluviatilis, Delphinus delphis, Tursiops truncatus and Lagenorhynchus acutus) were obtained from fresh tissue or from the NCBI GenBank and were used to perform a phylogenetic analysis with the blue whale (Balaenoptera musculus) sequence as an outgroup. Two base pairs substitutions were observed between the mtDNA sequence of the unidentified individual and the sequence of a S. longirostris from Fernando de Noronha Island, and nine differences were found between it and a same species of dolphin from North Atlantic, while 17 substitutions were reported between this dolphin and S. clymene. These results confirm that the dolphin from Bahia is a spinner dolphin. Phylogenetic analysis using maximum parsimony supported the results. This paper is an example of how molecular genetics can be useful to solve problems of identification of marine mammals.

Narrow barred Spanish mackerel is a high-value pelagic fish and is mostly caught in Bone Bay waters. These fish can be caught using purse seines, drift gill nets, lift net and hand lines, but the most catches are in drift gill nets and hand lines. This study aims to compare the performance of drift gill nets and hand line technologies. Biological, technical, social, economic and legal data were collected from 2018 to 2020 through direct field observations and interviews. Performance according to the four aspects and the combination of all aspects of the two fishing gear were analyzed using the Mangkusubroto Scoring method. Based on the biological and technical aspects the performance of the hand line was better than the drift gill nets, while on the contrary, based on the economic and social aspects, the performance of gill nets was better than the hand lines. Based on legal and institutional aspects, the two technologies do not show any differences. Although there are differences in the performance of the biological, technical, social and economic aspects, the performance of the two technologies is classified as good.

Conservation challenges for small-scale fisheries: Bycatch and habitat impacts of traps and gillnets

Although Fraser's dolphins Lagenodelphis hosei are considered to inhabit deep tropical waters worldwide, their occurrence in the tropical eastern Atlantic Ocean from the Gulf of Guinea southwards to Angola is only represented by two specimen records from Ghana. During cetacean surveys carried out concurrently with geophysical seismic surveys off Nigeria in 2004 and off Angola in 2007 and 2008, a pod of 150 probable Fraser's dolphins was videoed 130 km south of Nigeria and schools of 120 and 60 animals were photographed 170 km and 140 km respectively off the coast of Angola. All records occurred in deep water (>1 000 m). Cetacean bycatch was monitored at six artisanal Ghanaian fishing ports between 1998 and 2000. Four Fraser's dolphin specimens comprising one adult, one juvenile and two calves were photographed at two ports. Drift gillnets were identified as the probable cause of mortality for at least two specimens. Two sightings of Fraser's dolphins off Angola provide the first at-sea records for the Gulf of Guinea region and, together with bycaught specimens, confirm new southern and eastern distribution limits for the species within the Atlantic Ocean. Further information is required on the status of Fraser's dolphins and the potential impact of fisheries bycatch on this species within the Gulf of Guinea.

Neritic tuna is an important fishery commodity in the Java Sea, however, the availability of data and information on the fisheries characteristics is still limited. The study was conducted in 2018. Data was collected by researchers with the help of enumerators who monitoring and collecting data from the fishermen. The method used is direct observation at the study site and interviews with fishermen. This study aims to analyze information fishery characteristics in catch, catch per unit effort (CPUE), catch composition, fishing grounds, fishing season. The results show that neritic tuna in Java Sea caught by purse seine, mini purse seine, drift gillnet, and encircling gill net. The annual catch and CPUE of neritic tuna are still fluctuating. This tuna neritic fishery condition was showed that has not been overfishing. Catch composition of purse seine and mini purse seine dominated by small pelagic seine while catch composition drifts gill net and encircling gill net dominated by neritic tuna. The fishing ground around west of Karimun island, while purse seine from west of Bawean, Masalembu and around Matasiri island. Fishing seasons are April to May and October to December.

Brucella-exposure and infection is increasingly recognized in marine mammals worldwide. To better understand the epidemiology and health impacts of Brucella spp. in marine mammals of Brazil, molecular (conventional PCR and/or real-time PCR), serological (Rose Bengal Test [RBT], Competitive [c]ELISA, Serum Agglutination Test [SAT]), pathological, immunohistochemical (IHC) and/or microbiological investigations were conducted in samples of 129 stranded or by-caught marine mammals (orders Cetartiodactyla [n=124], Carnivora [n=4] and Sirenia [n=1]). Previous serological tests performed on available sera of 27 of the 129 animals (26 cetaceans and one manatee), indicated 10 seropositive cetaceans. Conventional PCR and/or real-time PCR performed in cases with available organs (n=119) and/or blood or swabs (n=10) revealed 4/129 (3.1%) Brucella-infected cetaceans (one of them with positive serology; the remaining three with no available sera). Pathological, IHC and/or microbiological analyses conducted in PCR/real-time PCR and/or seropositive cases (n=13) revealed Brucella-type lesions, including meningitis/meningoencephalitis, pneumonia, necrotizing hepatitis, pericarditis and osteoarthritis in some of those animals, and positive IHC was found in all of them (excepting two live-stranded animals without available organs). Brucella spp. culture attempts were unsuccessful. Our results demonstrated exposure, asymptomatic, acute and chronic Brucella sp. infection in several cetacean species in the Brazilian coast, highlighting the role of this pathogen in stranding and/or death, particularly in Clymene dolphin (Stenella clymene) and short-finned pilot whale (Globicephala macrorhynchus) off Ceará State. Novel hosts susceptible to Brucella included the franciscana (Pontoporia blainvillei), the Guiana dolphin (Sotalia guianensis) and the spinner dolphin (Stenella longirostris). Additionally, three coinfection cases involving Brucella spp. and cetacean morbillivirus, Edwarsiella tarda and Proteus mirabilis were detected. To the best of our knowledge, this is the first long-term and large-scale survey of Brucella spp. in marine mammals of South America, widening the spectrum of susceptible hosts and geographical distribution range of this agent with zoonotic potential.

Metazoan parasites of cetaceans off the northeastern coast of Brazil

Genetic analysis of Anisakis typica (Nematoda: Anisakidae) from cetaceans of the northeast coast of Brazil: New data on its definitive hosts

Ecological niche modeling of Stenella dolphins (Cetartiodactyla: Delphinidae) in the southwestern Atlantic Ocean