Diet of six deep-sea grenadiers (Macrouridae)

Feeding habits of six deep-sea demersal trawl-caught macrourids on Chatham Rise, New Zealand, were examined from stomach contents during the austral summer. Three species were predominantly benthic foragers: smallbanded rattail Coelorinchus parvifasciatus on small epifaunal crustaceans, twosaddle rattail Coelorinchus biclinozonalis on epifaunal decapods and humpback rattail Coryphaenoides dossenus on benthic fishes and epifaunal decapods. Three species were predominantly benthopelagic foragers: banded rattail Coelorinchus fasciatus on hyperiid and gammarid amphipods and calanoid copepods, blackspot rattail Lucigadus nigromaculatus on small epifaunal crustaceans and suprabenthic mysids and Mahia rattail Coelorinchus matamua on epifaunal decapods and calanoid copepods. The most important predictors of diet variability were identified using distance-based linear models and included areal predictors in C. parvifasciatus, L. nigromaculatus and C. dossenus, fish size in C. dossenus, C. biclinozonalis and C. matamua, sample year in C. biclinozonalis and C. fasciatus and depth in C. matamua. Results are compared with previously published data for four other macrourid species from the same study area. The 10 grenadier species comprise benthic, benthopelagic and mesopelagic foraging guilds. This study brings the number of grenadier species for which diet on Chatham Rise has been described in detail to 12.     

Three genera of myxosporida (Protozoa) in macrourid fishes

Three genera and eight species, three new, of myxosporida were recovered from seven genera and twenty species of geographically dispersed macrourid fishes. The constancy in spore dimensions of these species over large distances and among many host species was remarkable. Two genera of myxosporida had species which dwelled in both the gall bladder and urinary bladder/kidney.     

The biology of the bigeye grenadier at South Georgia

The biology of the bigeye grenadier Macrourus holotrachys caught as by‐catch in the Patagonian toothfish Dissostichus eleginoides longline fishery conducted around South Georgia was investigated to improve data available for fisheries management. Age estimates suggest that M. holotrachys is a moderately slow growing species ( K  = 0·10), reaching ages of >30 years and attaining total lengths ( L _T) >80 cm ( L _∞ = 33). The size at which 50% of females had started to mature ( L _int50) for M. holotrachys was 21 cm pre‐anal length ( L _PA) and occurred at c . 9 years old. Estimates of natural mortality and Pauly's growth performance index were found to be low ( M  = 0·09 and Φ = 2·82 respectively). Gonad maturity stage was described from macroscopic and histological investigation. Mature ovaries had oocytes at all developmental stages with between 22 and 55% likely to be spawned each year. Absolute fecundity ranged from 22 000 to 260 000 eggs and was positively correlated with both pre‐anal length and mass. A highly skewed sex ratio of 32 : 1, females : males, was found for specimens caught by longlines but not for a small sample of shallower trawl‐caught specimens. It is suggested that females are far more susceptible to longline capture than males. Macrourus holotrachys is a bentho‐pelagic predator and scavenger that feeds on a wide range of fishes and invertebrates. The fish are long lived, slow‐growing species typical of deep‐water grenadiers; fisheries management strategies should reflect their probable susceptibility to overfishing.     

Submarine canyons: hotspots of benthic biomass and productivity in the deep sea

Submarine canyons are dramatic and widespread topographic features crossing continental and island margins in all oceans. Canyons can be sites of enhanced organic-matter flux and deposition through entrainment of coastal detrital export, dense shelf-water cascade, channelling of resuspended particulate material and focusing of sediment deposition. Despite their unusual ecological characteristics and global distribution along oceanic continental margins, only scattered information is available about the influence of submarine canyons on deep-sea ecosystem structure and productivity. Here, we show that deep-sea canyons such as the Kaikoura Canyon on the eastern New Zealand margin (42°01′ S, 173°03′ E) can sustain enormous biomasses of infaunal megabenthic invertebrates over large areas. Our reported biomass values are 100-fold higher than those previously reported for deep-sea (non-chemosynthetic) habitats below 500 m in the ocean. We also present evidence from deep-sea-towed camera images that areas in the canyon that have the extraordinary benthic biomass also harbour high abundances of macrourid (rattail) fishes likely to be feeding on the macro- and megabenthos. Bottom-trawl catch data also indicate that the Kaikoura Canyon has dramatically higher abundances of benthic-feeding fishes than adjacent slopes. Our results demonstrate that the Kaikoura Canyon is one of the most productive habitats described so far in the deep sea. A new global inventory suggests there are at least 660 submarine canyons worldwide, approximately 100 of which could be biomass hotspots similar to the Kaikoura Canyon. The importance of such deep-sea canyons as potential hotspots of production and commercial fisheries yields merits substantial further study.     

Zschokkella (Protozoa: Myxosporida) in macrourid fishes

Six species of Zschokkella, three new, were recovered from eleven genera and forty-three species of macrourid fishes found in both the Atlantic and Pacific Oceans and many adjacent seas. The constancy in spore size and shape, over great distances and among many hosts, was remarkable.     

Preliminary survey of egg envelope morphology in the Macrouridae and the possible implications of its ornamentation

The eggs of only 13 macrourid species have been reported hitherto, eight identified from free buoyant eggs and five from ripening oocytes. Eggs of 11 species had raised, hexagonally patterned ornamentation on the envelope, while two species bore only partial ornamentation. Ripening oocytes of a further eight species showed that, overall, the eggs of 13 species had characteristic hexagonal ornamentation and three partial ornamentation, but four were smooth. Fertilized eggs of Coryphaenoides (Coryphaenoides) rupestris were found with smooth envelopes, while ornamented eggs have been reported for this species also. Little taxonomic significance could be attached to these results. Some correlation was found between the three categories of egg envelope ornamentation and species' bathymetric distributions. A recent model of egg development in a slope dwelling trachichthyid species suggested analagous potential ecological advantage for ornamentational variation in macrourids.     

Liparid and macrourid fishes of the hadal zone: in situ observations of activity and feeding behaviour

Using baited camera landers, the first images of living fishes were recorded in the hadal zone (6000–11 000 m) in the Pacific Ocean. The widespread abyssal macrourid Coryphaenoides yaquinae was observed at a new depth record of approximately 7000 m in the Japan Trench. Two endemic species of liparid were observed at similar depths: Pseudoliparis amblystomopsis in the Japan Trench and Notoliparis kermadecensis in the Kermadec Trench. From these observations, we have documented swimming and feeding behaviour of these species and derived the first estimates of hadal fish abundance. The liparids intercepted bait within 100–200 min but were observed to preferentially feed on scavenging amphipods. Notoliparis kermadecensis act as top predators in the hadal food web, exhibiting up to nine suction-feeding events per minute. Both species showed distinctive swimming gaits: P. amblystomopsis (mean length 22.5 cm) displayed a mean tail-beat frequency of 0.47 Hz and mean caudal : pectoral frequency ratio of 0.76, whereas N. kermadecensis (mean length 31.5 cm) displayed respective values of 1.04 and 2.08 Hz. Despite living at extreme depths, these endemic liparids exhibit similar activity levels compared with shallow-water liparids.