Behavior ecology of the Humboldt squid, Dosidicus gigas: insights from an animal-borne video and data logging system

Dosidicus gigas is a large pelagic cephalopod of the eastern Pacific that has recently undergone an unexpected, significant range expansion up the coast of North America. The impact that such a range expansion is expected to have on local fisheries and marine ecosystems has motivated a thorough study of this top predator, a squid whose lifestyle has been quite mysterious until recently. Unfortunately, Dosidicus spends daylight hours at depths prohibitive to making observations without significant artificial interference. Observations of this squid‟s natural behaviors have thus far been considerably limited by the bright illumination and loud noises of remotely-operated-vehicles, or else the presence of humans from boats or with SCUBA. However, recent technological innovations have allowed for observations to take place in the absence of humans, or significant human intrusion, through the use of animal-borne devices such as National Geographic‟s CRITTERCAM. Utilizing the advanced video recording and data logging technology of this device, this study seeks to characterize unknown components of Dosidicus gigas behavior at depth. Data from two successful CRITTERCAM deployments reveal an assortment of new observations concerning Dosidicus lifestyle. Tri-axial accelerometers enable a confident description of Dosidicus orientation during ascents, descents, and depth maintenance behavior - previously not possible with simple depth tags. Video documentation of intraspecific interactions between Dosidicus permits the identification of ten chromatic components, a previously undescribed basal chromatic behavior, and multiple distinct body postures. And finally, based on visualizations of spermatophore release by D. gigas and repetitive behavior patterns between squid pairs, this thesis proposes the existence of a new mating behavior in Dosidicus. This study intends to provide the first glimpse into the natural behavior of Dosidicus, establishing the groundwork for a comprehensive ethogram to be supported with data from future CRITTERCAM deployments. Cataloguing these behaviors will be useful in accounting for Dosidicus‟ current range expansion in the northeast Pacific, as well as to inform public interest in the impacts this expansion will have on local fisheries and marine ecosystems.

Comparative feeding ecology of two elasmobranch species, Squalus blainville and Scyliorhinus canicula, off the coast of Portugal

The small-spotted catshark (Scyliorhinus canicula) (Linnaeus, 1758) and the longnose spurdog (Squalus blainville) (Risso, 1826) are two species occurring in the European and western African continental shelves with a wide geographical distribution. In this study, the diet of S. blainville and S. canicula off the Portuguese western Atlantic coast was investigated in 2006 by collecting monthly samples of these two species from local fishing vessels. In the stomachs of both species, crustaceans and teleosts were the dominant prey items, and molluscs, polychaetes, echinoderms, and sipunculids were found in lower abundance. In S. canicula, urochordate and chondrichthyan species were also observed in stomachs and were classified as accidental prey items. Scyliorhinus canicula consumed a broader group of prey items than did S. blainville. A significant diet overlap was observed, despite both species occupying different depth ranges over the continental shelf. Scyliorhinus canicula exhibited a consistency in diet composition among seasons, sexes, and maturity stages. Nonetheless, for both adults and juveniles, an increase in relative abundance of teleosts in the diet was observed in the spring and summer. This study provides evidence of the importance of S. canicula and S. blainville as benthic and pelagic predators along the western Atlantic coast.

Regional variation in the annual feeding cycle of juvenile walleye pollock (Theragra chalcogramma) in the western Gulf of Alaska

Juvenile fish in temperate coastal oceans exhibit an annual cycle of feeding, and within this cycle, poor wintertime feeding can reduce body growth, condition, and perhaps survival, especially in food-poor areas. We examined the stomach contents of juvenile walleye pollock (Theragra chalcogramma) to explain previously observed seasonal and regional variation in juvenile body condition. Juvenile walleye pollock (1732 fish, 37–250 mm standard length) of the 2000 year class were collected from three regions in the Gulf of Alaska (Kodiak, Semidi, and Shumagin) representing an area of the continental shelf of ca. 100,000 km2 during four seasons (August 2000 to September 2001). Mean stomach content weight (SCW, 0.72% somatic body weight) decreased with fish body length except from winter to summer 2001. Euphausiids composed 61% of SCW and were the main determinant of seasonal change in the diets of fish in the Kodiak and Semidi regions. Before and during winter, SCW and the euphausiid dietary component were highest in the Kodiak region. Bioenergetics modeling indicated a relatively high growth rate for Kodiak juveniles during winter (0.33 mm standard length/d). After winter, Shumagin juveniles had relatively high SCW and, unlike the Kodiak and Semidi juveniles, exhibited no reduction in the euphausiid dietary component. These patterns explain previous seasonal and regional differences in body condition. We hypothesize that high-quality feeding locations (and perhaps nursery areas) shift seasonally in response to the availability of euphausiid

Feeding ecology of juvenile Pacific salmon (Oncorhynchus spp.) in a northeast Pacific fjord: diet, availability of zooplankton, selectivity for prey, and potential competition for prey resources

We investigated the feeding ecology of juvenile salmon during the critical early life-history stage of transition from shallow to deep marine waters by sampling two stations (190 m and 60 m deep) in a northeast Pacific fjord (Dabob Bay, WA) between May 1985 and October 1987. Four species of Pacific salmon—Oncorhynchus keta (chum) , O. tshawytscha (Chinook), O. gorbuscha (pink), and O. kisutch (coho)—were examined for stomach contents. Diets of these fishes varied temporally, spatially, and between species, but were dominated by insects, euphausiids, and decapod larvae. Zooplankton assemblages and dry weights differed between stations, and less so between years. Salmon often demonstrated strongly positive or negative selection for specific prey types: copepods were far more abundant in the zooplankton than in the diet, whereas Insecta, Araneae, Cephalapoda, Teleostei, and Ctenophora were more abundant in the diet than in the plankton. Overall diet overlap was highest for Chinook and coho salmon (mean=77.9%)—species that seldom were found together. Chum and Chinook salmon were found together the most frequently, but diet overlap was lower (38.8%) and zooplankton biomass was not correlated with their gut fullness (%body weight). Thus, despite occasional occurrences of significant diet overlap between salmon species, our results indicate that interspecific competition among juvenile salmon does not occur in Dabob Bay.

Feeding ecology of Atlantic bluefin tuna (Thunnus thynnus) in North Carolina: diet, daily ration, and consumption of Atlantic menhaden (Brevoortia tyrannus)

Diet, gastric evacuation rates, daily ration, and population-level prey demand of bluefin tuna (Thunnus thynnus) were estimated in the continental shelf waters off North Carolina. Bluefin tuna stomachs were collected from commercial fishermen during the late fall and winter months of 2003–04, 2004–05, and 2005–06. Diel patterns in mean gut fullness values were used to estimate gastric evacuation rates. Daily ration determined from mean gut fullness values and gastric evacuation rates was used, along with bluefin tuna population size and residency times, to estimate population-level consumption by bluefin tuna on Atlantic menhaden (Brevoortia tyrannus). Bluefin tuna diet (n= 448) was dominated by Atlantic menhaden; other teleosts, portunid crabs, and squid were of mostly minor importance. The time required to empty the stomach after peak gut fullness was estimated to be ~20 hours. Daily ration estimates were approximately 2% of body weight per day. At current western Atlantic population levels, bluefin tuna predation on Atlantic menhaden is minimal compared to predation by other known predators and the numbers taken in commercial harvest. Bluefin tuna appear to occupy coastal waters in North Carolina during winter to prey upon Atlantic menhaden. Thus, changes in the Atlantic menhaden stock status or distribution would alter the winter foraging locations of bluefin

The repulsive and feeding-deterrent effects of electropositive metals on juvenile sandbar sharks (Carcharhinus plumbeus)

Reducing shark bycatch and depredation (i.e., damage caused by sharks to gear, bait, and desired fish species) in pelagic longline fisheries targeting tunas and swordfish is a priority. Electropositive metals (i.e., a mixture of the lanthanide elements lanthanum, cerium, neodymium, and praseodymium) have been shown to deter spiny dogfish (Squalus acanthias, primarily a coastal species) from attacking bait, presumably because of interactions with the electroreceptive system of this shark. We undertook to determine the possible effectiveness of electropositive metals for reducing the interactions of pelagic sharks with longline gear, using sandbar sharks (Carcharhinus plumbeus, family Carcharhinidae) as a model species. The presence of electropositive metal deterred feeding in groups of juvenile sandbar sharks and altered the swimming patterns of individuals in the absence of food motivation (these individuals generally avoided approaching electropositive metal closer than ~100 cm). The former effect was relatively short-lived however; primarily (we assume) because competition with other individuals increased feeding motivation. In field trials with bottom longline gear, electropositive metal placed within ~10 cm of the hooks reduced the catch of sandbar sharks by approximately two thirds, compared to the catch on hooks in the proximity of plastic pieces of similar dimensions. Electropositive metals therefore appear to have the potential to reduce shark interactions in pelagic longline fisheries, although the optimal mass, shape, composition, and distance to baited hooks remain to be determined.

Geographical differences in the feeding patterns of red rockfish (Sebastes capensis) along South American coasts

Feeding habits and feeding strategy of red rockfish (Sebastes capensis) were studied from fish captured along most of the range of this species in coastal waters of South America. Stomach contents of 613 individuals, collected during 2003, were analyzed. Fish were obtained from six locations along the Chilean (23°S to 46°S) and Argentinian (43°S) coasts. The main prey items were Mysidacea (75.06% IRI), Osteichthyes (6.29% IRI),and Rhynchocinetes typus (6.03% IRI). Predator sex and size did not significantly affect the diet, but significant differences were found between locations. Four geographical areas, discriminated by prey occurrence and frequencies, were determined: three on the Pacific coast and one on the Atlantic coast. These areas correspond roughly with biogeographic zones described for the Chilean and southern Argentinian coasts. The feeding strategy index (FSI) indicated a specialized feeding strategy for S. capensis for most of its range. However, the FSI does not include the behaviour of a predator, and the FSI must be interpreted carefully for fishes like S. capensis that are passive ambush feeders. The abundance and availability of different prey may explain both the geographic differences in dietary composition and the specialized feeding strategy of S. capensis.

Reducing feed costs in semi-intensive finfish culture: an update on mixed feeding schedules and an idea for enhancing endogenous food supply in ponds

Some interesting ideas on improving the cost-effectiveness of feeding in semi-intensive finfish aquaculture are presented.

The introduction of exotic fish in Sri Lanka with special reference to tilapia

Introductions of exotic finfish between 1948 and 1953 are reported in this paper, with a brief reference to earlier and later introductions. Exotic fish were introduced principally to develop the potential for aquaculture in fresh and brackish waters in order to increase the availability of fish for rural communities through the biological control of aquatic vegetation. The algal feeding tilapia (Sarotherodon mossambicus) has created a new food industry in inland and brackishwaters. It has supplemented marine fishery production in a community where animal protein intake consists mainly of fish. It is also being cultured in flooded rice fields and used in the control of malaria. This excellent table fish has not had any adverse environmental impact.

Chemoreception studies in relation to feeding responses in the marine shrimps H. Milne Edwards (Penaeus indicus) and Miers (Metapenaeus dobsonii)

A study of chemoreception in relation to feeding and other factors involved showed that feeding behavior in shrimps can be triggered by chemical stimuli. However, Penaeus indicus and Metapenaeus dobsoni differ significantly in their chemotactic response to different stimuli.

Diet and feeding ecology of two sizes of Barbodes gonionotus (=Puntius gonionotus) and Oreochromis sp. in ricefields in Bangladesh

Fish culture experiments were conducted to compare and evaluate the feeding pattern and strategies, daily ration, gastric evacuation rates, dietary breadth, similarity and overlap of silver barb, Barbodes gonionotus, and tilapia, Oreochromis sp. (natural hybrid of O. mossambicus x O. niloticus) in a rice-fish system. B. gonionotus was found to be a macrophtophagous column feeder while Oreochromis sp. was a detrivorous benthophagic browser. Ontogenic shifts in diet were clearly observed in B. gonionotus while absent in Oreochromis sp. For both species, daily food ration for the small fish was twice as large as that for the large fish. Mean rates of gastric evacuation were 0.18 h super(1) for small and 0.05 h super(1) for large B. gonionotus and 0.09 h super(1) and 0.14h super(1) for small and large Oreochromis sp., respectively. In terms of intraspecific dietary width, the smaller sized individuals of both species had a wider dietary niche than the larger conspecifics. Larger fish increased their specialization and reliance on few food items with increasing size and competitive ability. When both species were reared together, B. gonionotus showed a wider niche width than tilapia. Wider interspecific niche width of B. gonionotus compared to that of tilapia and significant interspecific dietary overlap is likely to result in suppression of the growth of tilapia in mixed culture due to: 1) a high degree of specialization and reliance of tilapia on food of low-nutrient value, and 2) slower gastric evacuation rates as compared to B. gonionotus, which would allow B. gonionotus to outgrow similar sized tilapia.

Effect of substituting animal protein sources with soybean meal in diets of Oreochromis karongae (Trewavas 1941)

Three diets were formulated using locally available feed ingredients in Malawi to test the effect of replacing animal protein (fish meal, meat and bone meal) with soybean meal (10:0, 5:5, 0:10% of diet) as the protein source on growth and feed conversion of Oreochromis karongae. There were no significant differences in growth rate (GR), specific growth rate (SGR) and feed conversion ratios (FCR) among the three diets. It can be concluded that more expensive and limited animal protein sources can totally be replaced by cheaper soybean in order to get similar growth rates in O. karongae.

Food and feeding habits of Synodontis nigrita from the Osun River, SW Nigeria

An investigation was conducted into the food and feeding habits of Synodontis nigrita from the Osun River near Epe, Lagos, Nigeria. The food items in the stomach of the S. nigrita covered a wide spectrum, ranging from various types of plankton to invertebrates and plants. A seasonal variation was also noted in the stomach contents of S. nigrita over the period of investigation. The predominant food items found in the stomach were Polycystis spp., Closterium spp., Oedogonium spp., plant tissues, insect parts and detritus. This suggests that S. nigrita is an omnivore.

A preliminary study on the feeding regime of European pilchard (Sardina pilchardus Walbaum 1792) in Izmir Bay, Turkey, Eastern Aegean Sea

The gut contents of Sardina pilchardus specimens captured in Izmir Bay were examined in order to determine their feeding regimes. Of the 365 stomachs examined, 321 (87.95%) contained food and 44 (12.05%) were empty. Analysis of gut contents verified that S. pilchardus feeds on zooplankton. The most important group in the diet of S. pilchardus was copepods (79.79%). Decapod crustacean larvae (8.17%) and bivalves (3.18%) were second and third, respectively, in order of importance. The application of analysis of variance to monthly data of numerical percentage, weight percentage, frequency of occurrence and index of relative importance indicated that there was no significant difference between months. Oncaea media was the most dominant species for six months of the year. Euterpina acutifrons, Centropages typicus, Calanoida, Oncaea sp. and Corycaeus sp. were the most dominant for March, April, May, September, October and December.

Study on feeding habits of Piaractus mesopotamicus (Pacu) larvae in fish ponds

A limnological study of the artificial fish pond and an analysis of the stomach contents of pacu (Piaractus mesopotamicus) larvae of 2 to 45 days age were made for a period of 45 days to evaluate their feeding preferences. A preference for chlorophytes and rotifers were noted, while other planktonic species remained constant in the stomach contents. Some limnological variables were found to have strong influence on the feeding behavior of the pacu. A preference for feeding on smaller species in the first few days of larval development was also noted.