Feeding and digestion periodicity of Manila clam Ruditapes philippinarum in natural intertidal and subtidal zones estimated from the morphological condition of the crystalline style

ABSTRACT Feeding periodicities and rhythms of suspension-feeding bivalves in coastal waters are closely related to diel and tidal cyclic environmental changes, such as food availability and predation risk. Although such feeding periodicities of bivalves are important for understanding how their feeding strategies adapt to localized habitats, the feeding periodicity in bivalves in the field remains to be clarified, especially in infaunal species. The present study focused on the morphological condition of the crystalline style as an indicator of the feeding activity of the infaunal bivalve Manila clam, Ruditapes philippinarum, and estimated their feeding periodicity in the field. First, the effects of feeding (siphon-extending) behaviour, food and the light/dark cycle on the condition of the crystalline style (defined based on its morphology and hardness) were investigated in the laboratory. Results of the ordered logistic models and model selection showed that clams extending their siphons kept their crystalline styles hard. Furthermore, the effects of the light/dark cycle and tidal phase on the condition of the crystalline style were investigated in natural intertidal and subtidal zones and assessed using the results of the ordered logistic models. In the intertidal zone, the effect of the tidal phase was significant, whereas the effect of the light/dark cycle was not, and feeding was estimated to be active at ebb and flood tides, when the density of food particles was likely to be high. On the other hand, in the subtidal zone, the results of the model selection were not clear because of significant effects of interactions between the light/dark cycle and tidal phase. However, when the interactions were removed from the models, the effect of the light/dark cycle was significant, and feeding was estimated to be active at night when the predation risk from visual predators would be relatively low. These results confirm that R. philippinarum possesses behavioural plasticity in feeding periodicity, which is adaptable to both intertidal and subtidal zones.

Ignoring the vertical dimension: biased view on feeding dynamics of vertically migrating sprat (Sprattus sprattus)

Diel vertical migration (DVM) is a common behaviour and often relates with the diurnal feeding periodicity. Nonetheless, sprat feeding behaviour and daily ration (DR) estimation are usually based on daytime stomach contents from deeper layers. Our study provides a new approach for DR estimation, taking into consideration the DVM associated feeding periodicity. We analysed sprat DVM by hydroacoustics and collected stomach contents in the Central Baltic Sea at different depths. The main outcome is that feeding in the deep during the day represents only 16–39% of the DR. DRs were 1.4-times higher using our approach compared to the established approach. The underestimation by the established approach was mainly caused by ignoring the effect of higher temperatures from the upper layers on the gastric evacuation rate. Our results have major implications not only for DR estimates but also on the interpretation of prey selectivity. The study emphasizes the importance of adapting the sampling design to the vertical feeding dynamics to avoid a biased picture of predator prey interactions.

Spatial Distribution, Behaviour, and Biological Aspect of Albacore (Thunnus alalunga) Caught in Eastern Indian Ocean

This study highlighted the occurrence of the Indonesian tuna longline fishery targeting albacore (Thunnus alalunga) caught in the Eastern Indian ocean. The data used in this study based on the Research Institute for Tuna Fisheries (RITF) observer program in Benoa. This paper presents the current information on biological aspect (size distribution and length-weight relationship) and fish behavior (swimming layer and feeding periodicity) of albacore. Total albacore samples of 3,152 were taken from scientific observer data from 2010-2013. The study area of albacore was between 0-33°S and 75-131°E. Albacore length distributed from 70-196 cmFL (median=93 cmFL, mode=100 cmFL, mean=92.12 cmFL) and dominated at size of 95 cmFL. The highest percentage length of albacore was >90 cm (L50) occured in the area between (30-35°S and 80-95°E) and (10-15°S and 120-125°E). The length weight relationship was determined to be W=0.0045 FL1.8211 (W in kg, FL in cm). The expected season to catch the ALB was from April to July with the peak season in June and July. The swimming layer of albacore based on minilogger data were distributed from at 118 to 341 m depth and mostly catch at depth of 156 m with temperature degree 18°C. The feeding periodicity of albacore’s are start from 7:45am to 17:59 pm, mostly active at 10 am to 11 am. The majority of ALB caught by Indonesian longliner was mature condition and negative allometric growth. The ALB peak season was in June-July and the best time to catch was 10 am to 11 am at depth of 156 m. Keywords : albacore, feeding periodicity, swimming layer, CPUE

Diet Composition, Feeding Periodicity, and Prey Selection of Slimy Sculpin During Winter

Slimy Sculpin Cottus cognatus is an important component of the benthic ichthyofauna of many lakes and streams in the northern latitudes of North America. Although considerable information exists on the feeding ecology of this species, there is essentially no information available on winter feeding. Consequently, we examined the winter feeding ecology of Slimy Sculpins in a central New York stream. Ephemeropterans (37.8%) and trichopterans (31.2%) were the primary prey taxa consumed in January. There was evidence of diel variation in diet composition, with ephemeropterans making up 24.1% of the diet at 0400 hours and 46.7% at 1600 hours and trichopterans contributing 22.7% at 1200 hours and 43.8% at 2000 hours. During winter, Slimy Sculpins selected chironomids (0.46) and trichopterans (0.43) and avoided coleopterans (−0.84) and nonchironomid dipterans (−0.67). Peak food consumption of Slimy Sculpins occurred at night. Winter feeding patterns of Slimy Sculpins in Grout Brook, a second-order tributary of Skaneateles Lake in central New York, contrasted sharply with observations from other studies carried out during other seasons. Our findings are a significant contribution on the winter feeding ecology of this important benthic species and illustrate the need for both diel and winter studies to fully understand life history characteristics.

Feeding Ecology of Brook Silverside, Golden Shiner, and Subyearling Pumpkinseed in a Lake Ontario Embayment

Fish feeding ecology has been shown to vary over a 24-h period in terms of the prey consumed and feeding intensity. Consequently, in order to best determine the interspecific feeding associations within a fish community, examination of the diet at multiple times over a 24-h period is often necessary. We examined the diel feeding ecology of three fish species that were numerically dominant in a Lake Ontario embayment during summer. The diet of each of the three species, young-of-year Pumpkinseed Lepomis gibbosus, Golden Shiner Notemigonus crysoleucas, and Brook Silverside Labidesthes sicculus, was distinct with no significant overlap in diet composition occurring within any of the 4-h time intervals. The diet composition of each species suggested that Brook Silverside were feeding at the surface (terrestrial invertebrates and aquatic surface dwelling hemipterans), whereas young-of-year Pumpkinseed (amphipods) and Golden Shiner (tipulids) were feeding on different benthic prey. Differences in feeding periodicity were most pronounced for young-of-year Pumpkinseed. Our findings provide valuable insights on interspecific feeding associations among these three fish species during summer in a Lake Ontario embayment.

KEDALAMAN RENANG DAN WAKTU MAKAN IKAN ALBAKORA (Thunnus alalunga) DI SAMUDERA HINDIA SEBELAH SELATAN JAWA

Albakora adalah salah satu spesies tuna yang berupa hasil tangkapan beku bernilai ekonomis tinggi bagi kapal-kapal rawai tuna. Penangkapan albakora di Samudera Hindia semakin kompetitif, sehingga setiap nahkoda dan nelayan kapal rawai tuna perlu memiliki pengetahuanmengenai tingkah laku ikan seperti kedalaman renang dan waktu makan. Penelitian ini dilakukan dengan metode observasi langsung di atas kapal rawai tuna yang berbasis di Benoa dan Palabuhanratu sebanyak 3 trip mulaiMaret sampai Nopember 2013. Tujuan penelitian ini adalah untuk mengetahui kedalaman renang dan waktu makan albakora di Samudera Hindia. Hasil penelitian menunjukkan bahwa kedalaman renang albakora berdasarkan pengamatan data minilogger berada pada kisaran 57,04 - 325,46 m. Albakora lebih banyak tertangkap pada lapisan renang permukaan hingga pertengahan. Intensitas kebiasaan albakora mencarimakanan dilakukan antara pukul 07:45 - 17:59, dengan frekuensi tertinggi aktifmakan yaitu pada selang pukul 10:00 - 11:00. Untukmendapatkan hasil tangkapan albakora yang berlimpah, maka nelayan rawai tuna perlumenggunakanmetode penangkapan dengan perpaduan tipe rawai tuna permukaan dan pertengahan. Pengaturan waktu setting yang dimulai pagi hari dan waktu hauling mulai sore hari adalah waktu yang ideal dalampenangkapan albakora di Samudera Hindia.Albacore is one of the tuna species and mostly landed as frozen catch on tuna longliner. Albacore fishing in Indian Ocean more competitive, so Fishermans or Fishing Masters of tuna longliner must have knowledge of tuna behavior such as swimming layer and feeding periodicity. Research was conducted with observation on board on tuna longliner based Benoa and Palabuhanratu, totally 3 trips during March until November 2013. The aim of research are to know of swimming layer and feeding periodicity of albacore in Indian Ocean. Theresults showed that the swimming layer of albacore based minilogger data are distributed at 57.04 to 325.46 m The results showed that the swimming layer of albacore at 57.04 to 325.46 m. Albacore mostly catched in surface layer to middle in Indian Ocean. The feeding periodicity of albacore’s are start from 7:45pm to 17:59pm, mostly active at 10pmto 11pm. For the maximum catch of albacore’s, every fisherman of tuna longline must have a good fishing tactics. The combination of surface and middle tuna longline types are the best fishing tactics to be applied. The setting of tuna longline begin morning and hauling begin afternoon are the best time for fishing of albacore in the Indian Ocean.