Southern Garfish - Feeding Habits of South Australian Populations.

[MAH 438]

This information is based on the Honours thesis undertaken by Jason Earl in 2007, through Flinders University. All credit goes Jason for this knowledge.

The information is based upon samples of southern sea garfish that were collected at two locations in Gulf St. Vincent between March and July 2007. Most sampling was conducted at Port Parham, while fewer samples were also taken from Bay of Shoals, Kangaroo Island. Garfish were sampled for this study in two ways: they were purchased from commercial fishers after haul-net capture; and captured at night using dab nets. Hook and line were not used to capture the fish, as the use of foreign dietary items such as burley and bait would have disrupted the analysis of dietary composition. A total of 20 sampling events were undertaken.

The study found that the size of the mouth’s gape, the length of the beak and gut length were all proportional to fish size and these proportions are consistent over time, which does not suggest a major change in the feeding biology from juvenile stages through to adulthood.

The primary dietary components identified were seagrasses of the family Zosteraceae and planktonic amphipods.

Seagrasses were consumed in much greater volume than any other dietary item, followed by amphipods that were also consumed in high volumes. The high volumes of seagrass, may be due to the low nutritional value of seagrass and the inefficient digestion. To compensate for this, southern sea garfish may have to continually consume seagrass to maintain adequate nutrient absorption. Examining the gut contents showed the green, heavily macerated condition of the seagrass was consistently fresh throughout the entire study suggesting that rather than consuming floating detached seagrass fronds, as previously documented , the species may be grazing on live fronds. This assumption is supported by the observations of a commercial fisherman of Port Parham who regularly observed the species actively swimming through live fronds of the zosteraceaen seagrass beds in the area. If this is actually occurring it suggests that the fish are actively biting off seagrass fronds.

Other invertebrates such as polychaetes, insects and other crustaceans were a regular part of the diet, but only in smaller volumes.

Southern sea garfish appear to be selectively choosing their main dietary components, of zosteracean seagrass and amphipods.

Given the diversity of algae and different species of seagrasses distributed throughout the inter- and subtidal areas of the northern Gulf St. Vincent, the garfish that were sampled had exclusively consumed Zosteraceaen seagrasses.

Similarly, plankton tows that were done in the main sampling area at Port Parham revealed many types of hyperbenthic invertebrates available for consumption, yet the consistent consumption of large volumes of amphipods suggests that they were selected by the fish over other food.

The feeding patterns of southern sea garfish followed a strong diurnal cycle; consuming seagrass fronds during the day, to predation of hyperbenthic planktonic invertebrates during the night. The shift from seagrass, which is an unlimited, highly accessible resource, to the nocturnal consumption of invertebrates, coincided with significantly higher abundances of invertebrates in the water column during the night. Hyperbenthic invertebrate species occupy seagrass beds or the sediment during the day to avoid predation and then migrate vertically up into the water column during the night, to facilitate feeding and reproduction.

The study was conducted over autumn and winter and throughout both seasons the diets were dominated by seagrass during the day, before shifting to planktonic invertebrates during the night. Amphipods were the main invertebrates consumed during the night in both seasons while ostracods, cumaceans and nereidid polychaetes were also consumed at various stages. The most significant difference in dietary composition between seasons was the consumption of cirratulid polychaete worms during the early hours of the morning during winter. This species of worm was not apparent in the guts during autumn, but during winter was a very important component of the diet. It is not known whether the worms were excavated by the fish from the substrate or had migrated into the water column.

The feeding habits of the South Australian population of garfish are consistent with the findings for the Victorian population, however comparison between the diets of fish from Port Parham and Kangaroo Island provided some indication for regional variation. While nocturnal predation of amphipods was evident at midnight in fish captured from Port Parham, samples obtained from The Bay of Shoals, Kangaroo Island at the same time of the night contained large volumes of zosteracean seagrass and indicates the results from one area are not directly applicable to other areas where the availability of dietary components may differ.

[Wert 470]

I seriously love this stuff, it explains why they love a gent or small piece of prawn and are always covering everything in their poop,  keep em coming.

[Des 818]

Wonderfull information 

It can't but help your curiosity and wonder:

On 13/4/2022 at 1:53 PM, MAH said:

The feeding patterns of southern sea garfish followed a strong diurnal cycle; consuming seagrass fronds during the day, to predation of hyperbenthic planktonic invertebrates during the night. The shift from seagrass, which is an unlimited, highly accessible resource, to the nocturnal consumption of invertebrates, coincided with significantly higher abundances of invertebrates in the water column during the night.

Do all our regular baits like maggots, silverfish, chicken or pilchard slivers etc. work better at night?

Is there a seagrass type bait that can be used very effectively in the day time?

[Des 818]

 

Maybe saving all their poop and coating it over the other baits my well be an answer

On 13/4/2022 at 1:53 PM, MAH said:

Examining the gut contents showed the green, heavily macerated condition of the seagrass was consistently fresh throughout the entire study