<p>Natural and constructed rocky
reef habitats constitute important areas for lithophilic spawning fishes and
their embryonic and larval offspring. Interstitial spaces created by the
structure of rocky reefs create micro-environments where incubating embryos and
juvenile fishes are potentially protected from predators. However, if
interstitial spaces are filled or blocked by sediment deposition or biofouling,
the reef structure may lose the protective benefits for embryonic and larval fish
survival. Lake whitefish (<i>Coregonus clupeaformis</i>) and walleye (<i>Sander vitreus</i>) are native Great Lake
lithophilic broadcast spawning fish that use rocky spawning habitats that are
vulnerable to degradation caused by deposition of suspended sediments. To
restore degraded rocky reef habitat, common practices include addition of
material to existing reef structures or construction of new reefs, but both of
these practices can be costly and time intensive. In this study, we measured the
effect of different types and amounts of sediment cover on hatching success of walleye
eggs and assessed if differences in female walleye (female length and egg size)
account for tolerance to sediment cover. Additionally, we explored an
alternative approach for reef restoration, custodial maintenance, in which we
created two novel devices to potentially clean rocky reef habitat. We carried
out two laboratory experiments in 2018 and 2019 to test the effect of sediment
cover on hatching success of walleye eggs (2018) and to test how female
identity and female length or egg size may interact with sediment cover to
influence hatching success (2019). We exposed walleye eggs to instantaneous
sediment cover (0 mm – 7mm) of either sand (course) or silt (fine) sediments
from fertilization until day 15 of incubation. Our results indicated that walleye
eggs were sensitive to silt cover (71% mortality- 2 mm cover silt) but not sand
(47% mortality- 7mm cover sand). While there was an indication that hatching
success was marginally related to female length and egg size, we concluded that
sediment cover seemed to have similar effects on eggs, regardless of female
length or egg size. The susceptibility of walleye eggs to mortality caused by
sediment cover underscores the need for non-degraded spawning habitat. Our two
cleaning devices used either propulsion or pressurized water jets to clean
sediments from the rocky structure as they were towed behind a small vessel
(i.e., did not require the use of SCUBA divers). We used devices to clean two
natural rocky reefs in Saginaw Bay, Lake Huron in 2018 and 2019. We measured
relative hardness before and after use of devices on cleaned and uncleaned
study plots to determine effectiveness of devices. In addition, we measured egg
deposition by fall (lake whitefish) and spring (walleye) lithophilic spawners
on study plots to determine potential differences in fish usage of cleaned and
uncleaned areas. We found that cleaning devices contributed to changes in
relative hardness among study plots. Egg deposition was also variable on study
plots but in general, egg deposition was consistently highest on treatment plots
cleaned by our device that used propulsion. The practicality of cleaning
devices was seemingly related to the magnitude of degradation of rocky reefs,
nevertheless, our results show that the use of these or similar devices may
potentially increase egg deposition by creating areas of higher-quality
habitat. While more testing is necessary to fully understand the potential of
our reef cleaning devices, this two-year study suggests that these devices may
be capable of restoring degraded rocky spawning habitat which could potentially
minimize the negative effects associated with sediment degradation on
lithophilic spawning fish.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/11253308 |
| Date | 29 November 2019 |
| Creators | Alexander J Gatch (8045354) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Negative_effects_of_sedimentation_on_lithophilic_spawning_fish_embryos_and_methods_to_potentially_mitigate_these_effects/11253308 |
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