1 Catchability coefficients, the pro's and con's of trawl analyses are considered in Volvenko (2000).2 Records of all species caught are provided in Table 2, Pakhomov et al. (2019) and Table 3 in Somov et al. (2020).

While conservation and fisheries management are often concerned with changes in population abundance and distribution, shifts in population age–size structure are commonly observed in response to human and environmental stressors. Chinook salmon (Oncorhynchus tshawytscha) have experienced widespread declines in mean age and size throughout their North American range. We investigated the consequences of declines in body size for spawner reproductive potential in terms of total egg mass per female. Our case study is the Yukon River where Chinook salmon have supported subsistence, commercial, and recreational fisheries. Using historical observations on individual body size from throughout the Yukon River and the relationship between female size and total egg mass from the Canadian portion, we estimate a decline in average female reproductive potential of 24%–35% since the 1970s. Because spawner abundances and the population sex ratio have not shown clear trends over time, our results suggest a reduced total population reproductive potential. Changes in spawner quality should be considered when developing management reference points, and conservation of population demographic structure may be necessary to sustain productive Chinook salmon systems.

Salmon are an important natural, economic, and cultural resource for many people across the northern Pacific Rim, including all five North Pacific Anadromous Fish Commission (NPAFC) member nations.Monitoring and understanding the status of salmon stocks is critical to the management and conservation of this shared resource, especially within the context of a changing and increasingly variable environment that these stocks interact in (e.g., ocean warming and ocean acidification).It is unclear what the future holds for our salmon populations, but we need to think about, and prepare for, the inevitable changes.

Stocking of native fishes is conducted to augment riverine fisheries in many parts of the world, yet most stocking activities are conducted without empirical information on their effectiveness or impacts. In the Murray–Darling Basin (MDB), Australia, stocking has been underway for several decades to maintain recreational fisheries. We stocked chemically tagged golden perch (Macquaria ambigua) fingerlings in three rivers to determine the proportions of stocked fish within populations of the species. Stocked sites were monitored for up to 5 years in the Murrumbidgee River, Edward River and Billabong Creek and non-stocked sites were monitored in the Murray River. Catch per unit effort of stocked year classes increased substantially in Billabong Creek, with stocked fish contributing 100 (2005), 79 (2006) and 92% (2007). Chemically tagged fish comprised 18–38% of the respective age classes in the Murrumbidgee and Edward rivers and there was little evidence of natural recruitment in the non-stocked Murray River. Tagged fish generally attained the legal minimum size within 4 years and had dispersed up to 60km from the original release location. Our results demonstrate that artificial stocking has the potential to strongly influence the abundance and population structure of golden perch in rivers of the MDB.

Recent studies have described nonlethally detectable techniques for externally marking fish with fluorescent compounds such as calcein. We describe the use of a portable fluorometer for the nonlethal quantitative measurement of fluorescence in calcein marked golden perch Macquaria ambigua. The results demonstrate that calcein marked fish could be unambiguously identified more than 2 years after marking when held in the laboratory; the body mass of the fish had increased from 0.8 to 1.3 g (median 1.0 g) to 6-44 g (median 11.1 g) over this period. Similarly, marked fish released into the wild at approximately 1 g were detected at up to 18 months postrelease and 66 g in weight. However, some deterioration in the detectability of the external marks was apparent in the larger fish recaptured from the wild. Based on these findings, we suggest that the technique has the potential to provide a practical and objective means of discriminating hatchery and wild fish under field conditions.

The influence of seawater trace element concentration and temperature on statolith chemistry of the giant Australian cuttlefish, Sepia apama, was compared between encapsulated embryos and recently hatched juveniles under controlled laboratory conditions. Seawater Sr/Ca and Ba/Ca were positively related to statolith Sr/Ca and Ba/Ca in embryos and hatchlings for all temperatures. For statoliths of embryos the effect of spiking increased at 14°C compared to 20°C but for hatchlings increased Sr/Ca and Ba/Ca ratios in statoliths were found at 20°C compared to 14°C. The results imply that the influence of seawater trace element concentration and temperature on statolith chemistry was driven by elemental discrimination as described by partition coefficients but was reversed between life history stages. Differences in respiration and haemocyanin between the two life history stages may influence elemental uptake and discrimination. Thus, the results of the present study indicate that differences in element uptake in statoliths can occur among life history stages of S. apama and must be considered when reconstructing environmental histories of S. apama and other statolith bearing organisms.

We investigated the effect of hypersaline conditions on the water chemistry of the Coorong Lagoon, the terminal estuary of Australia's largest river, and the otolith chemistry of a common fish within the system. Water samples and fish were collected from 10 sites along the Coorong, ranging in salinity from 5.8 to 123.4, on six occasions over 14 months. Water (Ca, Ba, Mg, Mn, and Sr) and otolith (Ba : Ca, Sr : Ca, Mg : Ca, Mn : Ca, Na : Ca, Li : Ca, δ13C, and δ18O) concentrations were measured. Water Sr, Mg, and Ca concentrations exhibited conservative behavior (i.e., concentrations increased with salinity). Water Ba concentration decreased from near‐freshwater to marine salinities followed by an increase from marine to hypersaline waters, a pattern not previously reported in the literature. Three of the six otolith element : Ca ratios and δ18O showed significant linear correlations with salinity, but the best fit model for Ba : Ca was a segmented regression with a breakpoint. Positive linear correlations were also found between otolith Ba : Ca and water Ba : Ca, as well as otolith Mg : Ca and water Mg : Ca. Results have implications for reconstructing past salinities inhabited by fish, because they imply that several elemental and isotopic ratios will be necessary to determine whether fish have inhabited, or been exposed to, hypersaline environments.

Magnesium is a commonly measured element in otolith chemistry analysis and is often included in the suite of elements used to discriminate fish from different environments. Poor relations between Mg in water and otolith chemistry are, however, often found. We examined the uptake of Mg into the otoliths of a freshwater fish (silver perch Bidyanus bidyanus), to determine the extent to which this element can be used to record previous environmental conditions. Silver perch fingerlings were reared for 30 days in water with four concentrations of Mg (14.5, 36.6, 52.1 and 69.6 mg L−1) and fed on a diet supplemented with a combination of natural Mg and enriched 26Mg at five concentrations (1496, 1626, 1902, 2005 and 2036 μg g−1). Enriched 26Mg was added to the diet to achieve a 26Mg/25Mg ratio that was different from the natural ratio, such that the relative contribution of water and diet to Mg incorporated into otoliths could be determined. Enriching the diet with 26Mg resulted in an isotope shift in the otolith of silver perch from the natural 26Mg/25Mg ratio of 1.10–1.42; however, this was not as high as the ratio in the diet (> 3.7) suggesting that the fish did not fully incorporate Mg from the diet. Water was the primary source of otolith Mg, contributing on average > 80% to otolith Mg (range 74–95%). The fact that Mg concentrations in the otolith did not change in response to Mg concentrations in the water or diet, indicates that Mg is likely physiologically regulated and therefore is not a reliable environmental indicator.

Chemical marking of otoliths via immersion in solutions of enriched stable isotopes provides a means of distinctively marking large batches of hatchery-produced fish. Four enriched stable isotopes (barium: Ba-137 and Ba-138; strontium: Sr-88; magnesium: Mg-24) were used individually and in combination to determine mark success and the ability to correctly classify 15 unique batch marks in the otoliths of larval Murray cod Maccullochella peelii. Marking with the enriched stable isotopes Ba-137, Ba-138, and Sr-88 (individually or in combination) produced clear and distinctive marks (98% mark success) with 93% of fish correctly classified to their respective isotope mark. Despite exposure of the fish to an altered Mg isotope ratio in the water, a corresponding shift in the otoliths was not observed (8% mark success), and many Mg-24-enriched fish were misclassified. Due to the low cost and minimal effects on hatchery protocols, the use of Sr and Ba isotopes to mark hatchery-reared fish at the larval stage has the potential to be a powerful tool in the production and management of a wide range of fish species.

A promising new method of marking larval freshwater fishes with enriched stable isotopes by means of injecting the maternal parent with the marking agent was investigated. The (138)Ba:(137)Ba ratios in the otoliths of larval golden perch Macquaria ambigua were compared to determine the effect of injecting female broodstock with different dosages of enriched (137)Ba at various times before spawning. There was 100% mark success in the progeny of fish injected with 20 microg g(-1) of enriched (137)Ba 24 h before inducing spawning with hormones and 40 microg g(-1) administered at the same time as inducement of spawning. Injection of 40 microg g(-1) enriched (137)Ba 21 days before spawning resulted in only 81% mark success and suggests rapid elimination of barium in M. ambigua. Injection with enriched (137)Ba did not significantly affect the fertilization rate, number of fertilized eggs or hatching rate compared with long-term hatchery records. These results suggest that transgenerational marking is an effective and affordable means of mass-marking larval fishes. Thousands of larval fishes can be permanently marked with a unique artificial isotopic mark via a single injection into the maternal parent, thus avoiding the handling of individual fishes or having to deal with chemical baths. Because no single mark or tagging method is suitable for all situations, transgenerational marking with enriched stable isotopes provides another method for researchers and managers to discriminate both hatchery-reared and wild fishes.

We conducted a series of osmotic induction procedures for marking golden perch Macquaria ambigua with calcein and alizarin red S (ARS), evaluated the factors that influenced mark quality, and tested for any effects on fish growth and mortality. Three aspects of the marking protocols were considered: immersion time in a 5% salt solution (0, 5, or 10 min), immersion time in the fluorescent dye (5 or 10 min), and concentration of the dye (low or high). Quantitative estimates of mark intensity using photographs of marked fish were made with image analysis software. Although there were some significant interactions between factors, salt immersion was generally the primary determinant of mark intensity, followed by dye concentration and dye immersion time. Fish marked with calcein did not have higher mortality rates than unmarked fish and had significantly higher growth rates. The highest-exposure ARS treatments resulted in higher mortality and lower growth rates than for unmarked fish. Following this result, a lower-exposure ARS marking protocol was tested, which resulted in no detectable effects on mortality or growth rates while still producing high-quality marks. Although further study of the long-term retention of marks under field conditions is required 10 understand the limitations of the chemical marking methods examined in this study, our results suggest that the methods would greatly enhance our knowledge of the outcomes of fish stocking.

Woodcock SH, Gillanders BM, Munro AR, McGovern F, Crook DA, Sanger AC. Using enriched stable isotopes of barium and magnesium to batch mark otoliths of larval golden perch (Macquaria ambigua, Richardson). Ecology of Freshwater Fish 2011: 20: 157–165. © 2010 John Wiley & Sons A/SAbstract – Enriched stable isotope immersion techniques were used to mark the otoliths of larval golden perch (Macquaria ambigua) immediately post‐hatch. Two experiments were undertaken: the first involved rearing larvae in water enriched with three concentrations of 137Ba for 1–5 days. Marks were produced in as little as 1 day; however, otolith isotope ratios reached equilibrium with the water in 5 days at 90 μg·l−1. The second experiment involved rearing larvae in isotope enriched water with combinations of stable isotopes of Ba and Mg for 4 days after hatching. Seven significantly different isotopic signatures were produced using three Ba isotopes, which were reflective of the water. Only slight differences were found in otoliths of larvae that were reared in combinations of Mg isotopes, which did not reflect the water chemistry. The length of golden perch at 3 weeks of age showed that isotope immersion did not negatively affect early growth.

Osmotic induction marking trials with alizarin red S (ARS) were conducted on golden perch Macquaria ambigua to evaluate the use of ARS as a lower-cost alternative to osmotic induction marking with calcein for producing external fluorescent marks on hatchery-produced fish. After a 10-min immersion in a 5% solution of salt, experimental groups of golden perch were rinsed for 5 s in freshwater and immersed for 10 min in either a 0.1% or 0.5% solution of ARS, whereas control groups were either left untreated or immersed in a 0.1% solution of ARS for 10 min without prior immersion in the salt solution. All fish treated in the 0.5% solution of ARS died within 5 min of immersion, but no mortalities were observed in any of the controls or fish treated with the 0.1% solution of ARS. External fluorescent marks were observed on both the osmotic induction-marked fish and the direct ARS immersion-marked fish 100 d after treatment, but the osmotic induction-marked fish possessed more intense marks. Clear marks remained visible on fish marked by osmotic induction 9 months after treatment. This study indicates that highly visible external marks can be produced through osmotic induction with ARS at a substantially lower cost than marks produced through osmotic induction with calcein. Although further refinement and testing are needed, we conclude that the method has considerable potential for use in the mass marking of fish.