Status of Southern Garfish in the Perth Region in 2010-2011 (Figure 1) and the Proportion of Fish Aged More Than Two Years Fell from 30 % to Less Than 5%
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Department of Primary Industries and Regional Development Newsletter No. 36 October 2017 Welcome to the RAP Newsletter, providing feedback on the data you are collecting and keeping you informed about what is happening at the Fisheries Division of the Department of Primary Industries and Regional Development. Status of southern garfish in the Perth region in 2010-2011 (Figure 1) and the proportion of fish aged more than two years fell from 30 % to less than 5%. The average length also declined. Considering the maximum reported age of 10 years for this species, the age structure of the Cockburn Sound stock in 2010-2011 was heavily ‘truncated’ Photo 1: Southern garfish. (i.e. older fish were absent from the In June 2017, the Perth metropolitan Cockburn Sound was in relatively population). area was closed to both recreational good condition. But, soon after this and commercial fishing for southern study was completed, the abundance 60% garfish (Hyporhamphus melanochir) of garfish began a steady decline. In 50% to help the local population recover. response to this decline we began 40% n=294 We would like to thank those of you a major assessment of the stock in 30% who have been assisting us to monitor mid-2009. Most of our biological 20% 10% garfish by donating fish or recording sampling to determine age/length/sex Percent frequency logbook data. Your data is essential to composition of fishery landings was 0% 0 1 2 3 4 5 6 7 8 9 10 our assessments. done in 2010-2011. We then spent Age (years) Fisheries Research Report 271 many hours in the lab trying to age the contains the results of our first garfish fish using the otoliths we had collected. stock assessment, completed in This was a challenge because garfish 60 2014 (http://www.fish.wa.gov.au/ otoliths are quite difficult to interpret, n=480 40 Documents/research_reports/frr271. although we eventually got the hang of it! pdf). Our assessments have been 20 updated annually since 2014 and the Proportion (%) latest findings are published in the 0 0 1 2 3 4 5 6 7 8 9 10 State of the Fisheries Report each Age (years) year. Here is a quick summary of our latest assessment. Figure 1. The age structure of southern garfish in Cockburn Sound in 1998 Slow decline since the late (previous study) (top) compared to 2009-2011 (bottom), showing the 1990s disappearance of older fish and Cockburn Sound has traditionally been a decline in the average age. Note: the Photo 2: Garfish egg found in Cockburn maximum age recorded for southern the main fishery for southern garfish Sound. Filaments used to attach the egg garfish is 10 years. in the West Coast Bioregion (WCB). to marine vegetation are clearly visible. About 80% of commercial landings and Garfish eggs are relatively large (3 mm The age data was used to estimate the 50% of recreational landings of this diameter). Photo: Jan Richards ‘instantaneous rate of total mortality’ species in the WCB have been taken in (Z) acting on the stock in 1998-1999 Cockburn Sound. We found the typical (most common) and 2010-2011. Z is equal to the age of garfish had declined, from sum of fishing mortality (F) plus natural A previous study in 1998-1999 two years in 1998-1999 to one year suggested the garfish population in mortality (M), i.e. Z = F + M. Continued on page 2 Continued from page 1 Garfish biology Southern garfish occurs across southern Z was estimated to be 0.90 per And then the heatwave Australia, including WA (Kalbarri year in 1998-1999 and 1.57 per struck…. southwards), SA, Victoria and Tasmania. year in 2010-2011 which, in non- It reaches a maximum length of 49 cm After our biological sampling in technical terms, means there was an and can live 10 years. Although this 2010-2011, we continued to annual survivorship (S) of 41% and species grows rapidly and attains maturity monitor catches and catch rates of 21%, respectively. Compared to the at a relatively young age (about a year), garfish in Cockburn Sound and the rate of survivorship experienced by it has some biological traits that make it broader Perth area. Commercial garfish ‘naturally’ (i.e. in an unfished relatively vulnerable to overfishing: population), which is 64% per year and recreational catch rates fell (Z = 0.44), the total mortality in sharply in 2012, and have remained Low fecundity: A female may spawn 2010-2011 was extremely high. at historically low levels since multiple batches of eggs during spring This suggested that fishing pressure (Figure 3). Overall trends suggest a and early summer. Batch fecundity in Cockburn Sound increased very substantial (perhaps 70-90%) increases with size, ranging from about substantially between 1998-1999 reduction in garfish abundance in 100 eggs per batch for a small (22 cm) and 2010-2011, resulting in a 50% this area since the late 1990s. female to about 4,000 eggs per batch decline in survivorship. Recruitment failure during the for a large (40 cm) female. This is a low ‘heatwave’ event in summer 2010/11 level of egg production compared to many In our assessments, we tend to focus appeared to have caused the other fish species, which can produce on the rate of fishing mortality (F), dramatic decline in catches between tens of thousands or millions of eggs. rather than Z or M, because this is 2011 and 2012. Low fecundity limits how fast a garfish the factor that we actively manage population can recover from depletion. catch rate (fish/hour) rate catch (i.e. we can adjust catch and/or 0.6 Recreational commercial Small populations: In each region, fishing effort which will alter F, but 200 recreational 0.4 we can’t change natural mortality). southern garfish occur as multiple, 100 0.2 small, sub-populations. For example, In 2010-2011, the estimated F Commercial substantially exceeded the limit (kg/day) rate catch Cockburn Sound is believed to host its 0 0.0 reference point for this stock (Figure own sub-population. In SA, researchers 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 have found discrete (non-mixing) garfish 2). This level of fishing pressure is Year populations less than 60 km apart. This considered unsustainable. Figure 3: Annual commercial catch rate situation arises because garfish have (standardised) and recreational catch limited dispersal. Small populations are 1.5 rate of southern garfish in Perth area from 1996 to 2016, indicating a large more vulnerable to depletion (by fishing or decline in abundance since the late natural factors) than larger populations. 1.0 1990s, and very low abundance since Limited dispersal: Garfish eggs attach 2011. The recreational catch rate is to seagrass or other aquatic vegetation Flimit calculated from RAP logbook data, only 0.5 available from 2006 onwards (Note: via filaments on the egg (see Photo 2). Fthreshold Fishing mortality(F) Ftarget the commercial fishery voluntarily The larval stage is completed inside the ceased targeting garfish in 2016). egg, and they hatch as tiny juveniles 0.0 Female Male Both (~7 mm). Due to the attached eggs, and In summary, our assessment absence of a planktonic larval stage, there Figure 2: Rate of fishing mortality (F) indicates that the garfish stock in is no dispersal during these early stages. for southern garfish in Cockburn Cockburn Sound had been declining Juveniles and adults tend to remain Sound in 2010-2011, estimated since the late 1990s, mainly due using the age structure of males, associated with seagrass habitat too, females and both sexes combined. to an unsustainable level of fishing and so an individual fish might spend its Note: each F estimate, including pressure (both commercial and entire lifetime within the same seagrass 95 per cent confidence interval, recreational). The very depleted state bed. Limited dispersal means little mixing is well above the limit reference of the stock made it vulnerable to between populations. If a local garfish level for this species, indicating collapse after poor recruitment during population is depleted, it may take a an unacceptable level of fishing the ‘marine heatwave’. Five years pressure. Differences in F suggest long time to recover because it will not male garfish experience a slightly later garfish abundance remained be replenished by fish arriving from other higher rate of mortality than females. extremely low in the Perth area, and stocks. there was no sign of stock recovery. Dependency on seagrass habitat: These findings were consistent with This indicated that management Southern garfish are considered another part of the assessment which intervention was required to help this ‘seagrass-dependent’ because seagrass estimated that the spawning stock stock recover. With a fishing ban now forms a significant part of their diet and biomass of garfish had been greatly in place, we will continue to monitor their eggs must attach to seagrass (or reduced, to around 20% of the ‘virgin’ garfish over the next few years to similar vegetation) to survive. Garfish (unfished) level in 2010-2011. detect signs of recovery. generally live near seagrass or other marine vegetation all their lives. Seagrass habitat is threatened by human activities (such as dredging, water pollution) in many areas including Cockburn Sound. Blue groper attitude Jeff Norriss The recreational fishing community on WA’s south coast has a protective attitude toward the western blue groper that live along the coastline. Some southerners reckon there is something different about blue groper that makes them inherently vulnerable and, as a result, fishing for blue groper is not encouraged. So what is different about blue groper, compared to the average fish? Growing to 40 kg, blue perhaps due to fishing, one of the local females responds groper is southern Australia’s by changing sex to replace him.