Academic Articles -- ޢިލްމީ ލިޔުންތަކުގެ ޖަމާ
Browse
3 results
Search Results
Item ޕެމްފިސް : ބައިއޮޑައިވަރސިޓީ އެޑިޝަން(މިނިސްޓްރީ އޮފް އެންވައިރަމެންޓް އެންޑް އެނަރޖީ, 2014-11) މިނިސްޓްރީ އޮފް އެންވައިރަމެންޓް އެންޑް އެނަރޖީ; Ministry of Environment and EnergyItem Does bathymetry drive coastal whale shark (rhincodon typus) aggregations?(PeerJ, 2018-06-08) Copping, Joshua P.; Stewart, Bryce D.; McClean, Colin J.; Hancock, James; Rees, RichardBackground. The whale shark (Rhincodon typus) is known to aggregate in a number of coastal locations globally, however what causes these aggregations to form where they do is largely unknown. This study examines whether bathymetry is an important driver of coastal aggregation locations for R. typus through bathymetry's effect on primary productivity and prey availability. This is a global study taking into account all coastal areas within R. typus' range. Methods. R. typus aggregation locations were identified through an extensive literature review. Global bathymetric data were compared at R. typus aggregation locations and a large random selection of non-aggregation areas. Generalised linear models were used to assess which bathymetric characteristic had the biggest influence on aggregation presence. Results. Aggregation sites were significantly shallower than non-aggregation sites and in closer proximity to deep water (the mesopelagic zone) by two orders of magnitude. Slope at aggregation sites was significantly steeper than non-aggregation sites. These three bathymetric variables were shown to have the biggest association with aggregation sites, with up to 88% of deviation explained by the GLMs. Discussion. The three key bathymetric characteristics similar at the aggregation sites are known to induce upwelling events, increase primary productivity and consequently attract numerous other filter feeding species. The location of aggregation sites in these key areas can be attributed to this increased prey availability, thought to be the main reason R. typus aggregations occur, extensively outlined in the literature. The proximity of aggregations to shallow areas such as reefs could also be an important factor why whale sharks thermoregulate after deep dives to feed. These findings increase our understanding of whale shark behaviour and may help guide the identification and conservation of further aggregation sites.Item Maldives pole-and-line tuna fishery : livebait fishery review 2015(Marine Research Section, Ministry of Fisheries and Agriculture, 2015) Jauharee, A. Riyaz; Neal, Ken; Miller, Kelsey I.; އޭ. ރިޔާޒް ޖައުހަރީ; ކެން ނީލް; ކެލްސީ އައި. މިލަރFishing for tuna is an important industry in the Maldives, providing employment for thousands of people and contributing up to 1.3% of GDP (NBS 2014). The pole-and-line fishery for tuna targets skipjack Katsuwonus pelamis , yellowfin Thunnus albacares and big eye Thunnus obesus . The pole-and-line fishery depends on livebait: small shoaling fish that are thrown alive into the water behind the fishing vessel to elicit a feeding response in the tuna and encourage them to attack the lures on line at the end of the poles whereupon they are flicked into the fishing vessel. These small fish are collected with rectangular lift nets, often using lights at night to lure them to the water’s surface, within atolls prior to each fishing trip in the open ocean and are kept alive on the fishing vessel in tanks in the vessels’ hold. The pole-and-line tuna fishery was accredited by the Marine Stewardship Council as being sustainable in 2012 but with eight conditions, one of which concerned the quantity of livebait being harvested and another with the interaction of endangered, threatened and protected species (ETP) with the livebait fishery. Since 2010, logbook data has been collected throughout the Maldives on the quantity and type of bait being collected by pole-and-line fishers as well as any interactions with ETP species. Initially, low numbers of logbook records were returned and therefore only data from 2011 onwards was included in the analysis. Logbook returns peaked in 2013 at over ten thousand records but not all of these could be used due to missing pieces of information. Nevertheless, once the data had been filtered for full records, many thousands of data points were used in the analysis. Silver sprat Spratelloides gracilis was the most important bait species throughout the Maldives with varying contributions to livebait catches from blue sprat Spratelloides delicatulus, anchovy Encrasicholina heteroloba, cardinalfish Apogonidae, fusiliers Caesionidae and species of Chromis. 7 Analysis of catches showed great variability in quantities of livebait between region, year and month. Statistical comparison of catches between years was impaired in many cases by lack of data, but many species showed either no significant difference in catches between years or a decrease from 2011 to 2014, depending on region. Importantly, any differences between years were not consistent by species or region and therefore changes in catches may be related to local depletion or inter-annual variability in abundance of these short-lived species rather than population-level effects of the bait fishery. Logbook data on interactions of the collection of bait fish with ETP species was lacking and therefore appraisal was made using that collected by independent observers of bait fishing operations. All indications are that ETP species are not harmed in any way by bait fishing and occasional entanglement or entrapment in the gear usually results in the organism in question being released without injury. Sharks and stingrays are an exception (not ETP species globally but do benefit from protection in the Maldivian waters) which occasionally suffer injury when being extracted from the nets used for collecting bait.