Partitioning of material discarded from Prawn Trawlers in Morton Bay

1990 ◽  
Vol 41 (1) ◽  
pp. 27 ◽  
Author(s):  
TJ Wassenberg ◽  
BJ Hill
Keyword(s):  
Water Column ◽  
Tursiops Truncatus ◽  
Portunus Pelagicus ◽  
Moreton Bay

Prawn trawlers in Moreton Bay, Queensland, discard about 3000 t of material each year. About 3% floats, and the rest sinks. The floating component is almost entirely fish. At night, floating discards are eaten by silver gulls (Larus novaehollandiae), crested terns (Sterna bergii) and, to a lesser extent, dolphins (Tursiops truncatus). There is little trawling during the day but the last discards are dumped overboard around dawn. At this time cormorants (Phalacrocorax varius) join the scavengers. Birds and dolphins scavenged only fish and cephalopods, and not crustaceans nor echinoderms. Birds are selective as to the size of fish they will eat, but most of the whole fish in the discards are below 50 g, and the largest fish that crested terns ate was 100 g. Dolphins are capable of taking the largest of the discarded fish. Most of the material that sinks is crustaceans (54%) and echinoderms (18%); the rest is elasmo- branchs and rubble. At night, about half of the fish that sink are eaten by diving birds and by dolphins. There was no indication of mid-water scavenging of sinking discards, except for cormorants and dolphins in the upper water column. Approximately 11% of the discards that reach the bottom comprise fish and crustaceans, which are eaten by crabs (Portunus pelagicus) and fish. The remainder- chiefly crabs, echinoderms and elasmobranchs-reach the bottom alive. Altogether, about 20% of discards are eaten by surface and bottom scavengers. Discards are probably important in maintaining populations of the major scavengers.

Evaluation of anchor tags for marking the commercial sand crab, Portunus pelagicus (L.) (Portunidae : Decapoda)

1986 ◽  
Vol 37 (6) ◽  
pp. 707 ◽  
Author(s):  
MJ Williams
Keyword(s):  
Population Studies ◽  
Field Trials ◽  
Short Term ◽  
Portunus Pelagicus ◽  
Term Survival ◽  
Return Rates ◽  
Moreton Bay ◽  
Short Term Survival

Laboratory and field trials of a modified Floy FD67 anchor tag were conducted on P. pelagicus in Moreton Bay, Queensland. The tags did not affect short-term survival of the crabs in the laboratory. Only 470 of 1754 crabs tagged and released in the field were returned. Return rates of crabs by size, sex, and area of tagging class were markedly heterogeneous. Poor visibility of the tags on recapture, regardless of their colour, makes this tag unsuitable for any quantitative population studies. Poor return rates were exacerbated by fishermen not examining categories of crabs that are unmarketable.

Parasitism of the commercial sand crab Portunus pelagicus (L.) by the rhizocephalan Sacculina granifera Boschma, 1973 in Moreton Bay, Queensland, Australia

1994 ◽  
Vol 45 (2) ◽  
pp. 169 ◽  
Author(s):  
WD Sumpton ◽  
MA Potter ◽  
GS Smith
Keyword(s):  
Adult Female ◽  
Egg Mass ◽  
Size Distributions ◽  
Adult Males ◽  
Infection Rates ◽  
Portunus Pelagicus ◽  
Female Population ◽  
Moreton Bay ◽  
Adult Females

In Moreton Bay, Queensland, externae of Sacculina granifera Boschma were found in 7.0% of adult males and 123% of adult females of Portunus pelagicus. Infection rates were seasonal for both sexes and higher in the adult female population, with more than 20% of adult females carrying externae during some summer months. Infection rates were less than 3% in areas outside the bay and generally highest in the southern and central bay. Nineteen males and 15 females had abdominal scars where externae had become dislodged. The gonads of most parasitized crabs were underdeveloped, but 5.6% of externa-bearing females and 10% of externa-bearing males also had well developed gonads. Two female sand crabs were found with both a small egg mass and a mature externa (a condition not previously reported). Size distributions of infected and uninfected adult crabs were similar, suggesting that large crabs as well as juvenile crabs were likely to be infected.

Tissue nutrient content of Gracilaria spp. (Rhodophyta) and water quality along an estuarine gradient

1995 ◽  
Vol 46 (6) ◽  
pp. 975 ◽  
Author(s):  
JL Horrocks ◽  
GR Stewart ◽  
WC Dennison
Keyword(s):  
Water Quality ◽  
Water Column ◽  
Plant Tissue ◽  
Time Course ◽  
Inorganic Nitrogen ◽  
River Mouth ◽  
Nutrient Content ◽  
Moreton Bay ◽  
Tissue Nutrient Content ◽  
Tissue Nitrogen

Tissue nutrient content of Gracilaria spp. (Rhodophyta) was tested as a bioindicator of water column nutrient availability in the Logan River and southern Moreton Bay, south-eastem Queensland. Macroalgae were incubated for one to two weeks within flow-through incubation chambers suspended in the water column. Tissue nutrient content of Gracilaria spp, and water column nutrients were measured at five sites over a five-month period. Tissue nitrogen content (%N) was correlated with dissolved inorganic nitrogen (DIN) at a site 15 km upstream from the Logan River mouth (r² = 0.81), at the Logan River mouth (r² = 0.50), and at a Moreton Bay site 8 km from the Logan River mouth (r² = 0.71). Time-course analyses of water column nutrients and plant tissue content showed more significant correlations with nitrogen (N) than with phosphorus (P). Plant tissue nitrogen-to-phosphorus (N:P) molar ratios ranged between 19 and 23 whereas water column N:P ratios were between 2 and 6, suggesting low nitrogen availability relative to plant requirements and possible N limitation. In the laboratory, Gracilaria verrucosa was subjected to treatments of N, P or N + P nutrient additions. Deepening of the thallus colouration was observed after additions of N. Chlorophyll and phycoerythrin concentrations increased in treatments with N addition; however, owing to wide variability between phycoerythrin replicates, only chlorophyll increases were significant. The amino acid citrulline also increased with the addition of N and accounted for up to 16% of the total tissue N. Macroalgae may be more useful than traditional water quality sampling for integrating biologically available pulses of nutrients, especially for a limiting nutrient such as N in coastal marine ecosystems.

Movement, fishery sector impact, and factors affecting the recapture rate of tagged sand crabs, Portunus pelagicus (L.), in Moreton Bay, Queensland

1991 ◽  
Vol 42 (6) ◽  
pp. 751 ◽  
Author(s):  
MA Potter ◽  
WD Sumpton ◽  
GS Smith
Keyword(s):  
Bacterial Infection ◽  
Spatial Heterogeneity ◽  
Fishing Effort ◽  
Mature Male ◽  
Short Term ◽  
Portunus Pelagicus ◽  
Term Survival ◽  
Factors Affecting ◽  
Moreton Bay ◽  
Short Term Survival

Selected mature male sand crabs (Portunus pelagicus) (6827 individuals with carapace widths of 120-192 mm) were tagged with Floy ED-68BA anchor tags and released in 14 areas of Moreton Bay and adjacent oceanic waters. In all, 1003 tagged crabs (14.7%) were recaptured, with 79% of these recaptured less than 2 km from their release points and 4% recaptured more than 10 km from their release points. Of the total recaptures, 63% were made within 14 days of crabs being released. Commercial pot fishers recaptured the largest proportion (70%) of crabs, whereas recreational fishers and commercial trawl fishers recaptured only 18 and 12% of tagged crabs, respectively. Recapture rates varied from 2 to 59%, depending on location, reflecting a massive spatial heterogeneity of fishing effort. Only 2.6% of recaptured crabs moulted between release and recapture. Crabs that were undamaged at release had twice the recapture rate of damaged crabs (i.e. crabs that had missing appendages), and the probability of recapture increased with crab size. Under laboratory conditions, unmodified Floy FD-68BA tags reduced the short-term survival of male P. pelagicus, possibly because of bacterial infection, and it was concluded that Floy anchor tags were not suitable for field growth studies of P. pelagicus.

Effect of temperature on the Emergence, activity and feeding of male and female Sand Crabs (Portunus pelagicus)

1990 ◽  
Vol 41 (4) ◽  
pp. 545 ◽  
Author(s):  
WD Sumpton ◽  
GS Smith
Keyword(s):  
Seasonal Changes ◽  
Sexual Differences ◽  
Effect Of Temperature ◽  
Catch Per Unit Effort ◽  
Portunus Pelagicus ◽  
Male And Female ◽  
Temperature Range ◽  
Moreton Bay ◽  
Trap Fishery ◽  
Food Consumed

The effect of temperature on emergence, activity and feeding of the sand crab, Portunus pelagicus (L.), was measured under laboratory conditions. Crab emergence was greatest at night, particularly shortly after dusk. Males were significantly more active than females, but the activity of both sexes declined with falling temperature. There were no significant differences in the amount of food consumed by male and female P. pelagicus within the temperature range 16.5-26�C. It was concluded that sexual differences in catchability, as a result of differential activity and feeding, were not responsible for the seasonal changes in catch per unit effort of male and female P. pelagicus in the Moreton Bay trap fishery.

The potential of benthic iron and phosphorus fluxes to support the growth of a bloom forming toxic cyanobacterium Lyngbya majuscula, Moreton Bay, Australia

2016 ◽  
Vol 67 (12) ◽  
pp. 1918 ◽  
Author(s):  
Peter Hanington ◽  
Andrew Rose ◽  
Ron Johnstone
Keyword(s):  
Water Column ◽  
Benthic Community ◽  
Sediment Cores ◽  
Community Change ◽  
Flood Event ◽  
Nutrient Fluxes ◽  
Marine Cyanobacterium ◽  
Lyngbya Majuscula ◽  
Moreton Bay ◽  
Sandy Sediments

Lyngbya majuscula is a bloom-forming toxic marine cyanobacterium. Most research on L. majuscula growth in Moreton Bay has focussed on water column supplies of iron and phosphorus with little consideration of benthic sources and supply. This study investigates the potential for sandy sediments in a shallow, well mixed subtropical embayment (Deception Bay, Moreton Bay, Australia) to supply iron and phosphorus for L. majuscula growth after significant benthic community change following a major flood event. Measurements of benthic oxygen, iron and nutrient fluxes were obtained by incubating intact sediment cores sampled from Deception Bay. Results suggest that post-flood sediment communities are capable of supplying >1300% of daily L. majuscula Fe requirements and up to 9.2% of daily P demands, suggesting that L. majuscula growth in Deception Bay is likely to be P limited. The benthic release of PO43– and FeII only occurred after water column DO became depleted below 3mgL–1. This study suggests that the benthic release of PO43– and FeII could support the initiation and growth of L. majuscula blooms in Deception Bay.

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