For many aquatic organisms, olfactory-mediated behaviour is essential to the maintenance of numerous fitness-enhancing activities, including foraging, reproduction and predator avoidance. Studies in both freshwater and marine ecosystems have demonstrated significant impacts of anthropogenic acidification on olfactory abilities of fish and macroinvertebrates, leading to impaired behavioural responses, with potentially far-reaching consequences to population dynamics and community structure. Whereas the ecological impacts of impaired olfactory-mediated behaviour may be similar between freshwater and marine ecosystems, the underlying mechanisms are quite distinct. In acidified freshwater, molecular change to chemical cues along with reduced olfaction sensitivity appear to be the primary causes of olfactory-mediated behavioural impairment. By contrast, experiments simulating future ocean acidification suggest that interference of high CO ₂ with brain neurotransmitter function is the primary cause for olfactory-mediated behavioural impairment in fish. Different physico-chemical characteristics between marine and freshwater systems are probably responsible for these distinct mechanisms of impairment, which, under globally rising CO ₂ levels, may lead to strikingly different consequences to olfaction. While fluctuations in pH may occur in both freshwater and marine ecosystems, marine habitat will remain alkaline despite future ocean acidification caused by globally rising CO ₂ levels. In this synthesis, we argue that ecosystem-specific mechanisms affecting olfaction need to be considered for effective management and conservation practices.

Non-lethal human disturbances are often drivers of change in animal population and community structure. To gauge their severity, short-term behaviour (e.g. avoidance and habituation) has been argued to be a sensitive measure. However, many of these behavioural changes may occur only if disturbance-free habitat is readily accessible. In coral-reef fish, we tested whether human disturbances from intensive (i.e. loud music, swimming, snorkelling, splashing and fish feeding by numerous visitors) tourist visitations resulted in assemblage structure shifts led by short-term behaviour. We monitored fish assemblage before, during and after tourist visitations to monitor changes associated with behaviour. Additionally, we monitored two adjacent reefs not visited by tourists because of difficult approach by boat. We posited that if short-term benefits of relocating to disturbance-free habitat outweigh the costs of tolerating disturbances, fish assemblage structure should shift along with tourist visitation levels. By contrast, if sensitive species are unable or unwilling to relocate, we predicted greater levels of assemblage heterogeneity between the visited and control reefs. Our results showed that in situ human visitations led to significant shifts in assemblage structure, resulting from short-term behavioural changes. Additionally, we showed significant between-reefs differences, whereby control reefs were characterised by higher species richness, larger fish sizes and variations in relative trophic guild prevalence. Our results suggest that short-term relocations to adjacent disturbance-free reefs may not mitigate the effects of human disturbances.

The incidental capture of threatened species as bycatch is placing global biodiversity at risk ([ 1 ][1], [ 2 ][2]), particularly in developing countries where small-scale fishing and hunting often rely on unselective capture methods ([ 3 ][3], [ 4 ][4]). To address this, the Indian Maharashtra state government recently announced that it will financially compensate fishers who release incidentally captured endangered species. Payment will be made based on photographic evidence of the captured individual and proof that fishing gear was damaged to allow the release ([ 5 ][5]). ![Figure][6] India is emulating Kenya's bycatch release program, which protects endangered green sea turtles. PHOTO: JOHN WARBURTON-LEE PHOTOGRAPHY/ALAMY STOCK PHOTO Financially incentivizing the release of threatened bycatch considers the needs of fishers and hunters whose actions often have direct consequences for conservation ([ 6 ][7], [ 7 ][8]). As a result of a similar pay-for-release program, Kenyan fishers have released about 17,000 threatened bycaught sea turtles over the past two decades ([ 8 ][9]). This positive outcome underscores clear and measurable conservation gains, yet pay-for-release schemes remain a rarely used conservation strategy. Instead, tackling the issue of bycatch mostly relies on modifying capture gear, education, and enforcing legislation ([ 1 ][1], [ 2 ][2], [ 9 ][10]), approaches that commonly require long-term investment for positive outcomes ([ 3 ][3], [ 4 ][4], [ 10 ][11]). The pay-for-release strategy could provide a rapid, complementary mechanism to ease pressure on threatened species, such as sawfishes ([ 11 ][12]), that are not the focus of harvest and require immediate conservation action ([ 5 ][5], [ 12 ][13]). The Maharashtra government, and any local governments that follow suit, should explore a broad range of scenarios and collect results to determine the most effective way to implement this type of program and to assess its effectiveness. 1. [↵][14]1. R. Lewison, 2. L. B. Crowder, 3. A. J. Read, 4. S. A. Freeman , Trends Ecol. Evol. 19, 598 (2004). [OpenUrl][15][CrossRef][16][Web of Science][17] 2. [↵][18]1. R. Corlett , Biotropica. 39, 292 (2007). [OpenUrl][19][CrossRef][20][Web of Science][21] 3. [↵][22]1. E. J. Milner-Gulland, 2. E. L. Bennett , Trends Ecol. Evol. 18, 351 (2003). [OpenUrl][23][CrossRef][24] 4. [↵][25]1. M. Becker et al ., Biol. Conserv. 158, 26 (2013). [OpenUrl][26] 5. [↵][27]1. C. Marpakwar , “Fisherman, who save rare marine animals caught in their nets to get compensation,” Mumbai Mirror (2018); . 6. [↵][28]1. P. J. Ferraro, 2. A. Kiss , Science 298, 1718 (2002). [OpenUrl][29][FREE Full Text][30] 7. [↵][31]1. M. R. W. Rands et al ., Science 329, 1298 (2010). [OpenUrl][32][Abstract/FREE Full Text][33] 8. [↵][34]Local Ocean Conservation, Bycatch Release (). 9. [↵][35]1. L. M. Komoroske, 2. R. L. Lewison , Front. Mar. Sci. 2, 1 (2015). [OpenUrl][36][CrossRef][37] 10. [↵][38]1. J. Senko, 2. E. R. White, 3. S. S. Heppell, 4. L. R. Gerber , Anim. Conserv. 17, 719 (2013). [OpenUrl][39] 11. [↵][40]1. L.R. Harrison, 2. N. K. Dulvy , “Sawfish: A global strategy for conservation” (IUCN Species Survival Commission's Shark Specialist Group, 2014). 12. [↵][41]1. A. O. H. C. Leduc, 2. N. E. Hussey , Conserv. Biol. 10.1111/cobi.13300 (2019). [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: #ref-5 [6]: pending:yes [7]: #ref-6 [8]: #ref-7 [9]: #ref-8 [10]: #ref-9 [11]: #ref-10 [12]: #ref-11 [13]: #ref-12 [14]: #xref-ref-1-1 "View reference 1 in text" [15]: {openurl}?query=rft.jtitle%253DTrends%2BEcol.%2BEvol.%26rft.volume%253D19%26rft.spage%253D598%26rft_id%253Dinfo%253Adoi%252F10.1016%252Fj.tree.2004.09.004%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [16]: /lookup/external-ref?access_num=10.1016/j.tree.2004.09.004&link_type=DOI [17]: /lookup/external-ref?access_num=000225033100009&link_type=ISI [18]: #xref-ref-2-1 "View reference 2 in text" [19]: {openurl}?query=rft.jtitle%253DBiotropica.%26rft.volume%253D39%26rft.spage%253D292%26rft_id%253Dinfo%253Adoi%252F10.1111%252Fj.1744-7429.2007.00271.x%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [20]: /lookup/external-ref?access_num=10.1111/j.1744-7429.2007.00271.x&link_type=DOI [21]: /lookup/external-ref?access_num=000245939300002&link_type=ISI [22]: #xref-ref-3-1 "View reference 3 in text" [23]: {openurl}?query=rft.jtitle%253DTrends%2BEcol.%2BEvol.%26rft.volume%253D18%26rft.spage%253D351%26rft.atitle%253DWILD%2BMEAT%253A%2BTHE%2BBIGGER%2BPICTURE%26rft_id%253Dinfo%253Adoi%252F10.1016%252FS0169-5347%252803%252900123-X%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [24]: /lookup/external-ref?access_num=10.1016/S0169-5347(03)00123-X&link_type=DOI [25]: #xref-ref-4-1 "View reference 4 in text" [26]: {openurl}?query=rft.jtitle%253DBiol.%2BConserv.%26rft.volume%253D158%26rft.spage%253D26%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [27]: #xref-ref-5-1 "View reference 5 in text" [28]: #xref-ref-6-1 "View reference 6 in text" [29]:...