Resource partitioning by two large planktivorous fishes Micromesistius australis and Macruronus magellanicus in the Southwest Atlantic

The ontogenetic, seasonal, bathymetric and regional variations in the feeding spectrum of 922 specimens of southern blue whiting Micromesistius australis and 512 specimens of hoki Macruronus magellanicus were studied on the Falkland Islands’ shelf (Southwest Atlantic) between November 1999 and April 2003. A total of 49 different prey items were found in the stomach contents of the two species, with the hyperiid Themisto gaudichaudii and Euphausiacea being amongst the most important prey. Although the species composition did not change over fish size, the proportions of individual prey items in their diets did, with an increase in T. gaudichaudii and Euphausiacea with increasing fish size in southern blue whiting. The opposite occurred in hoki. Seasonal variations in the diet were found to mirror the seasonal abundance of prey around the Falkland Islands for the two species. Intra-specific differences in the diet of both predators reflected the distribution of prey, which in turn was determined by the water structure in the two regions sampled, leading to very different diets. In the limited time that the two species occupied the same space there was little or no competition resulting in almost total segregation of their trophic niches in space and time.     

Growth of red gurnard (Teleostei: Triglidae) from Pegasus bay,Canterbury, New Zealand

Growth of the red gurnard, Chelidonichthys kumu (Lesson and Garnot), from Pegasus Bay, Canterbury, was measured during 1966–67. Otoliths were used as an indicator of fish growth; mean length‐at‐age data were obtained from back‐calculated fish lengths at the time of formation of successive annual rings in the otoliths. Growth in length was found to be adequately expressed by the von Bertalanffy growth equation :

l_t = 52.0 [1 ‐ e‐^{0.406 (t‐o.291)}]

(where l_t is the fork length in cm at age t). The length: weight relationship was:

w = 78.56 × 10^‐4 l ^3.072

(where w is the weight in grams). From this relationship, growth in weight was described by the equation:

w_t = 1469 [1 ‐ e‐0.406 (t‐0.291)]³.     

Limnology of Bird Pond,Ross Island,Antarctica

The physical, chemical and biological properties of Bird Pond, Cape Bird, Ross Island, Antarctica (77° 13’ 10” S, 166° 28’ 30” E), were investigated at weekly intervals for 2 months in the summer of 1970–71. The above properties were also investigated over a 24‐h period. Salinity and temperature tolerance of the rotifer Philodina gregaria were investigated in the laboratory at Cape Bird.

Bird Pond is characterised by a high conductivity and chloride ion concentration, and an alkaline pH. It has a water temperature as high as 15°c in mid summer, with the bottom water temperature often 3°c higher than the surface temperature. Diurnal measurements suggest a vertical movement of phytoplankton during a 24‐h period. P. gregaria survives ionic concentrations up to 250 000 g.m^‐3 Na⁺ + Cl^‐, and water temperatures up to 32°c.     

Comparison and history of Polydora websteri and P. haswelli (Polychaeta: Spionidae) as mud-blister worms in New Zealand shellfish

Shells of commercially valued bivalves in New Zealand, Crassostrea gigas, Perna canaliculus and Pecten novaezelandiae, are damaged by blister-causing Polydora polychaete species known to be close in morphology to the widely recorded oyster pest Polydora websteri Hartman. Recent New Zealand occurrences are here confirmed to relate to two species, P. websteri, and a second similar species, Polydora haswelli Blake & Kudenov, a new record for New Zealand, previously known only from Australia; the two species are described and compared. The worms have limited distributions, with P. websteri confirmed only for Pacific oysters (C. gigas) in northern New Zealand, although prior reports indicate it may also occur on scallops and have reached the northern South Island. Polydora haswelli has been found only in northern New Zealand, occurring on subtidal mussels and scallops and native oysters (Perna canaliculus, Pecten novaezelandiae, Ostrea chilensis), as well as co-existing with intertidal P. websteri on Pacific oysters. The worms are not present in Foveaux Strait O. chilensis beds, a major source of past oyster exports to Australia. The history of mud-blister worm outbreaks in Australasia is examined. While trans-Tasman exports of live oysters from New Zealand were commonplace during the nineteenth century, there is no evidence that mud-blister worms were present in New Zealand then. The earliest reports only date from the early 1970s and only from northern New Zealand, whereas a century earlier in the 1870s at least one of these pest worms had become widespread along eastern Australian coasts.     

Response of excised gill tissue from the New Zealand scallop Pecten novaezelandiae to suspended silt

The role of turbidity in scallop mortality was investigated for two size classes of Pecten novaezelandiae (70 ± 2 mm and 20 ± 1 mm shell height), by using the “crawl” velocity of excised pieces of gill tissue as an indicator of the response to suspended silt. The crawl velocity of 3 × 5 mm pieces of gill tissue was measured in six different silt concentrations (0.025, 0.05, 0.1, 0.2, 0.3. 0.5% silt, by dry weight) and two size classes (< 10 μm and 10–30 um) of silt. Results of the study indicate that juvenile (20 mm shell height) scallops may be less tolerant of suspended silt than larger (70 mm shell height) scallops and that both size classes may be less tolerant of fine (< 10 μm) silt/clay sized particles than coarse (10–30 μm) particles. These conclusions are supported in part by data from the mortality of whole 20 mm scallops exposed to two size classes (< 10 μm and 10–30 μm) and three concentrations (0.05, 0.3, 0.6%, by dry weight) of silt. Increasing concentrations and decreasing particle size of the suspended silt resulted in reduced gill piece crawl velocity and an increase in the mortality rate of the whole scallops. These results suggest controls on human‐induced disturbance of bottom sediments, such as bottom trawling and dredging, may benefit any further scallop bed enhancement programmes by the avoidance of deterioration in water quality and mechanical damage to scallop spat.     

Sediments of lakes Rotoroa and Rotoiti,South Island,New Zealand

The chemistry and mineralogy of the sediments of Lakes Rotoroa and Rotoiti, South Island, New Zealand (41° 51 S, 172° 38 E and 41° 50 S, 172° 50 E respectively) , were studied. In general, the cation exchange properties, element concentrations, and mineral compositions of the sediments show little variation between samples from each lake. However, some nutrient concentrations, notably exchangeable calcium, magnesium, and potassium, and total nitrogen and sulphur, are higher in sediments from weed beds than in sediments underlying deeper water; iron and manganese concentrations tend to show the opposite trend. Concentrations of exchangeable calcium and total nitrogen, sulphur, manganese, and iron generally decrease down the sediment profiles from the sediment/water interface. Differences between lakes, notably higher concentrations of illite and of the elements potassium, aluminium, titanium, and zirconium, and lower concentrations of calcium in the sediments of Lake Rotoiti than in those from Lake Rotoroa, are probably due mainly to the different geological settings rather than to differences in the diagenetic processes operating within the lakes. Mineralogical analyses indicate that the lake sediments are derived mainly from the valleys of the major inflow rivers rather than from the slopes at the sides of each lake.     

The food and feeding of seven fish species from the Campbell Plateau,New Zealand

The food and feeding habits of hoki (Macruronus novaezelandiae), southern blue whiting (Micromesistius australis), javelin fish (Lepi‐dorhynchus denticulatus), ling (Genypterus blacodes), smooth rattail (Coelorinchus aspercephalus), silverside (Argentina elongata), and small‐scaled notothenid (Notothenia microlepidota) sampled from the Campbell Plateau in 1979 were examined. The importance of prey items in the diet has been assessed by an ‘index of relative importance’, which combines measurements of frequency of occurrence, number, and weight of prey. Hoki, southern blue whiting, and javelin fish are pelagic feeders. Hoki preyed largely on natant decapod crustaceans, amphipods, and myctophid and photichthyid fishes. The main prey of southern blue whiting were amphipods, natant decapods, and euphausiids. Javelin fish fed on natant decapods, amphipods, and small squid. Seasonal and regional differences in feeding, and dietary changes with length of fish were evident. Ling, smooth rattail, silverside, and small‐scaled notothenid are predominantly benthic feeders. Ling preyed on natant decapods, macrourid fishes, and small hoki. The diet of rattail comprised natant decapod crustaceans, opal fishes (Hemerocoetes spp.), and poly‐chaetes. Silverside fed almost solely on salps. Salps, amphipods, brachyuran crustaceans, and opal fishes were the main prey of small‐scaled notothenid.     

Validated aging methodology using otoliths,and growth parameters for hoki (Macruronus novaezelandiae) in New Zealand waters

The age of hoki was determined by counting bands in otolith cross‐sections. The technique was validated using the progression of length modes in length‐frequency distributions (for age classes 0+ to 4+) and the progression of strong and weak year classes in age‐frequency distributions from commercial catches sampled off the west coast of the South Island, New Zealand, from 1988 to 1994. Von Bertalanffy growth parameters for the west coast and Cook Strait spawning populations are significantly different, providing further support for a two‐stock hypothesis. In both areas female hoki have a growth rate significantly faster than males, and also a greater life expectancy.