In May, as a part of our year end recap, we sent this noticing and inquiry out to our partner teachers…
“Of the three Waikīkī streams we study, Mānoa has MORE sections of natural stream habitat than Pālolo and Makiki, but LESS presence of ʻoʻopu. Throughout 2023, we saw a higher instance of smallmouth bass in our nets in the lower sections of Mānoa Stream, but NONE in Pālolo and Makiki. Could bass, known as aggressive predators, be acting as a biological barrier to ʻoʻopu upstream migration in Mānoa? What further investigation can students do on this?”
We are pleased to report that ʻIolani School Independent Research student, Ann Tokoyoda, has joined forces with graduate student, Jaimie Hijii, from the Tsang Stream Lab at UH Mānoa, to investigate this issue further, and help provide our program with insight into bass diet.
With our whole Community Science team's support, Jaimieʻs background in bass aging research, and Annʻs experience with eDNA sequencing, we set out to examine the stomach contents of smallmouth bass caught in Mānoa Stream through both morphological and molecular techniques. Jaimie and Cory used a dissecting microscope in an attempt to find physical remains that could be morphologically identified as belonging to native ʻoʻopu and ōʻpae. At the same time, Ann collected samples from the stomach contents to use for DNA identification. Through dissection, we found the rostrum (comb-like portion of the head between the eyes resembling a nose or beak) and claw of an ʻōʻpae ʻoehaʻa, as well as what appeared to be the lower jawbone of an ʻoʻopu.
These tentative morphological identifications were confirmed through Annʻs sequencing; both ʻōʻpae ʻoehaʻa and ʻoʻopu akupa were identified in smallmouth bass stomach contents. Knowing more about the bassʻ preferred diet and how much their predation impacts ʻoʻopu populations will take more time and research to conclude.
However, confirming that they are eating our native species helps us more confidently discuss this problem with our partner teachers and students. While we cannot target specific species for removal directly through our fish population surveys with students, we can all initiate important conversations with our neighbors and the recreational fishing community about the negative impact of relocating invasive fish like bass into our streams and encourage more bass fishing in Mānoa to rectify the problem.
